Romania enters World War I
The Central Powers defeat Romania
27 August - 6 December 1916
author Paul Boșcu, July 2018
After a series of negotiations with the Entente, Romania declared war on the Central Powers and invaded the, then, Austro-Hungarian province of Transylvania. The Central Powers quickly mobilized their forces and ejected the Romanians from Transylvania, invading Romania from the west and south. At the end of the campaign the Romanian capital, Bucharest, fell into enemy hands. The Romanian government and what was left of their army had to retreat to the Romanian eastern province of Moldavia. There, with Russian support, they established new defensive lines.
After the Brusilov Offensive, Romania, which had been long courted by the Entente, but had until then chosen to stay neutral, entered the war. Romania’s primary goal was acquiring Transylvania from Austro-Hungary. Thus it was that the first military action of the Romanian army was the invasion of Transylvania through the Carpathian passes. The Central Powers response came swiftly, pushing the Romanians out of Transylvania and invading the country from the west and south. The capital, Bucharest, was conquered. All told, the Romanian interlude was a disaster for the Entente and a morale-boosting victory with very tangible rewards for the Central Powers.

Romania declared war on Austria-Hungary and promptly invaded Transylvania via the passes through the Carpathians and Transylvanian Alps. It would prove a momentous decision, but not quite in the way that the Romanians had hoped.

It soon became clear that the Romanian armies would be incapable of prolonged resistance. Even the wide waters of the Danube could not stop the Germans, while they eventually burst through the deep passes of the Transylvanian Alps. By then the hapless Romanians were in a state of collapse and there was nothing their new allies could do to help them.

The Germans entered Bucharest in triumph and the Romanians were forced to acknowledge defeat. The Ploiesti oil fields, thirty-five miles north of the capital, were also overrun, and they would prove an invaluable prize to the oil-starved Central Powers.

Over the next year the Germans would raid Romania for much-needed supplies of oil, grain, farm animals and wood, succeeding to an extent in defraying the inconveniences of the British blockade in the North Sea.

Italy’s entry into the war was from the start a mixed blessing, but in the spring of 1915 it looked quite promising, and at the end of the year, with Serbia occupied and the debris of the Serbian Army stranded in the Adriatic, the Entente looked around for another partner. Calculating everything by the gross, they decided that since Romania had a total military of nearly three quarters of a million men, and since Austria-Hungary was reeling on the verge of collapse, the entry into the war of hundreds of thousands of Romanians would be the straw that broke the camel’s back. This did not prove to be the case.

So long as the Central Powers appeared invincible, Romania could not risk intervening against them. Her strategic situation was peculiarly vulnerable. But with the great run of Russian victories, her confidence rose. Moreover, by August 1916, the western Powers were prepared to guarantee much more territory than before: the French, in particular, with an eye to the post-war situation, wanted to establish a greater Romania as a bulwark against Russia.

The Entente had long been wooing Romania, which had an interest in joining the war. This interest was Transylvania, Hungarian-ruled, but mostly Romanian-populated. However, Romania could only hope to get it if the Entente won, and up to mid-1916 that did not look very likely. Besides, should a Central Powers victory put Transylvania out of reach, Russian Bessarabia (now the Republic of Moldova), also mostly Romanian-populated, could be a consolation prize. Strategic vulnerability also dictated caution. Romania had very long frontiers relative to its area, and its neighbours from the West and South were already in the Central Powers camp.

Bulgaria had joined the Central Powers in September 1915, had a territorial claim against Romanian Dobrudja and could well pursue it militarily if Romania joined the Entente. Bucharest would then be particularly endangered, as it was only 30 miles (48 km) from the Bulgarian border.

Romania’s chief national interest was the addition to its territory of Transylvania, where three million ethnic Romanians lived under Austro-Hungarian rule. As Brusilov's advance pushed westward, widening the common border of military contact between Russia and Romania and apparently promising not only Russian support but Austrian collapse, the Romanian government's indecision diminished. Prudence probably dictated staying neutral, but General Brusilov's successes created a chance for Romania to seize Transylvania while Austria-Hungary was fully stretched. Thus Romania declared war.

Good sense should have told the Romanians that their strategic situation, pinioned between a hostile Bulgaria to the south and a hostile Austria-Hungary to their west and north, was too precarious to be offset by the possible support of a Russian army which had only belatedly returned to the offensive.

The Romanians had been following the war with interest, trying to figure out how they could benefit from it. As the example of Serbia had shown, there was no profit in tangling with the Austro-German-Bulgarian triad unless you had serious support. The Romanians were less than enthusiastic about their nearest potential supporter, Russia. For Romania to be persuaded to enter the war, the ‘bribe’ would have to be substantial.

Romania would be given Transylvania. In no case would the inhabitants of these areas be allowed to decide their fate; they were simply handed over. In order to bring Romania into the war, the Entente not only appealed to that nation’s greed, they then sweetened the deal by making promises of military support, which they ultimately did not keep and probably had no intention of keeping.

A military convention was signed, providing for extensive Entente assistance, both financial and military. The Romanian divisions would, it was thought, decisively affect the eastern front as a whole. In exchange, after the war Romania would receive territories from the defeated Austro-Hungary.

The Entente had long been offering an enlargement of Romania's territory at Austrian expense, following victory, and Romania, unwisely, now decided to take the plunge. A convention was signed by which France and Russia bound themselves to reward Romania, once peace was obtained, with Transylvania, Bukovina, the southern tail of Galicia, and Banat, the southwestern corner of Hungary.

The Entente’s analysis of German losses led them to the conclusion that Germany was on the verge of collapse. And thus the importance of Romania. Verdun was Germany’s last-ditch offensive. If it failed, Germany would collapse. How could it be made to collapse faster? Clearly only so much could be expected from Russia at this point. But Romania had a sizeable army, well in excess of half a million men, which could bring the Germans to their breaking point. The problem was that the Entente’s estimates of German capabilities were wrong, and the German army in 1916 was nowhere near its breaking point.

Austria was on the verge of collapse; Germany couldn’t fight the war on its own; Romania would be the straw that broke the camel’s back. If the Central Powers had been as enfeebled in the summer of 1916 as British and French intelligence insisted they were, the Romanian gambit would have worked.

It is not altogether easy to see why Entente leaders expected the intervention of small powers to be so decisive. No doubt it was an illusion that owed something to misreadings of Napoleonic history. The nationalistic vibrations of Madrid and Lisbon were thought to have shaken the French Empire to its foundations. In reality, nationalism had been much less important than the heavy pounding to which the French armies had been subjected in Austria and Russia; and the Peninsular War involved an army that was, by the standards of the time, large and efficient. The Romanian army could not stand comparison.

The Romanian army numbered 23 divisions, but all were poorly equipped and deficient in wheeled transport; the road system was inadequate, and the railways not much better. Most Romanian soldiers were illiterate and ill-trained. The officers lacked experience, and were also inclined to panic. As things turned out, it was the Russians, and not the Central Powers, who suffered from a Romanian ulcer. Almost a third of the Russian army had to be diverted to the south. This did not save Romania.

British observers felt that the operations of the Romanian Army would make a public-school field-day look like the execution of the Schlieffen Plan; while the comments of Russians who had to fight side-by-side with the Romanians were often unprintable.

Russian troops were pinned to the Kowel and Galician offensives; half of them were placed north of the Pripyat with almost nothing to do. Mikhail Alexeyev himself, the Russian Chief of Staff, had been told again and again that Romanian intervention would be decisive. Russian diplomats had been induced to promise Romania the areas of Austria-Hungary she coveted, and later on the Entente connived at Romania’s acquisition of Russian territory, Bessarabia. Alexeyev himself generally felt that Romanian intervention was not worth this much – on the contrary, it would be a liability.

At the turn of 1915-16, Alexeyev had opposed schemes for bringing Romania in – the front would be lengthened, southern Russia would thus be exposed to a German attack through Romania, the Russian army was not large enough to cover all of the area, and the Romanian army was useless.

In June, Alexeyev’s attitude had changed to some extent, but he was never willing to make sacrifices for Romania, and now preferred to concentrate his troops on Kowel and Lwów. In any case, the railway links between Russia and Romania were too weak to allow any rapid diversion of Russian troops. There were only two single-track lines connecting the two countries, and even then there was the usual problem of differing gauges.

Late in November, French General Joseph Joffre managed to extract from Alexeyev a promise that Russian troops would assist in the defense of Bucharest; but since the Romanians could not offer even the sixteen trains per day needed for these troops, the proposal fell through.

One division was left to guard Dobrudja, and almost all the rest were sent into Transylvania. Hungary had few troops there, a few days would suffice to take it, and then Dobrudja could be reinforced. However, as insurance, the Romanian High Command asked Russia for troops and Alexeyev agreed to send to Dobrudja the minimum three divisions specified by the Russo-Romanian military convention. Unfortunately, this proved only the first, and smallest, burden that Romania's entry into the war imposed on Russia.

Bulgaria was not at war with Russia, and diplomatic maneuver and a token military presence might deter it from invading Dobrudja. But Austria-Hungary and Germany were already at war, so diplomacy could not neutralize the threat from Galicia. To counter it, Alexeyev dispatched seven infantry divisions and one cavalry division to the Ninth Army, stationed in Galicia.

For Dobrudja, Alexeyev could spare only two Russian divisions, while the convention stipulated at least three. A '1st Serbian Volunteer Division' was being formed from prisoners of war, and Alexeyev decided to include it in the 'Dobrudja Detachment'. To find Russia allied with Romanians and Serbs, whom they had fought as recently as 1913, would extend Bulgarian hostility from them to their Russian mentors.

The Romanians nevertheless went to war in apparent high confidence in their army of twenty-three divisions, formed from their stolid peasantry, and in the belief that the Russian offensive north of the Pripet Marshes, towards Kovel, would prevent the transfer of German reserves towards Hungary, while Brusilov's continuing offensive would hold the Austrians in place.

The Romanians appeared to have made little allowance for the eventuality of Bulgarian or, as it came to pass, Turkish intervention. They also overestimated the military potentiality of their armed forces, which were poorly equipped and owed their reputation for fighting power to their success in the Second Balkan War at a moment when Bulgaria was hard pressed also by the Serbs, Greeks and Turks.

The army could be easily split up between different functions, each of them difficult to discharge. The Romanian High Command complicated this problem still more by failing to give constant priorities to the various strategic tasks. Half of the army was switched, bewilderingly, between one front and the other. Romania’s intervention could only matter if the initial offensive against Hungary won an immediate success. This did not turn out to be the case.

The Romanians opened an offensive, not, as the commanders in Salonika had expected, against Bulgaria, where it might have lent support to and been supported by their own, but into Hungary through the passes of the Transylvanian Alps. The Romanians occupied Southern Transylvania, but the Central Powers retaliated quickly.

Transylvania was a region with its own historic identity and a large German minority. Resistance to the Habsburgs over the centuries hardly meant that all of the natives would welcome the Romanians with open arms, particularly since some of the Romanian army’s habits of occupation more closely resembled those of a Mongol horde than a modern army.

Von Straussenburg, the Austrian local commander, rallied local militia, convalescing soldiers and regular army units sent to the area for refitting, together with the police (the Feldgendarmerie), and put up a surprisingly stout defense. Three weeks into September, the Romanians were still trying to fight their way out of southeastern Transylvania, and had failed to get much farther than Hermannstadt (present-day Sibiu). The delay was fatal for Romania. The German General Staff, which had been brooding about Romania’s possible entry into the war for some months, already had a plan developed to counter the threat.

Nearly 400,000 Romanians crossed the Hungarian borders. Frontier villages were occupied, together with the old Saxon town of Kronstadt (Brașov), which lay in the southeastern tip of Transylvania. But supply problems turned out to be crippling. There was not much railway communication between Hungary and Romania, and the little that existed was badly managed. The paths through the mountains could often only accommodate troops moving in single file, not carts or guns.

Romanian commanders behaved ineptly, and seemed to think that the prospect of meeting German troops dispensed them from further activity. Some of them even thought that, once they reached Central Transylvania, they would be so far from their supply routes that catastrophe would intervene. In consequence, the Romanians occupied the southeastern tip of Transylvania, and waited to see what would happen.

Newly installed as the German Chief of Staff, Paul von Hindenburg reacted immediately. He used the unified command established in the Eastern Front to good effect. Two armies were swiftly established from disparate elements of German, Austrian, Bulgarian and Turkish units: one, the Army of the Danube, was to be commanded by August von Mackensen and would invade Romania from their Bulgarian frontier in the south; the other, the German Ninth Army, would first rebuff the Romanian invasion of Transylvania, then invade Romania from the west. This would be led by Erich von Falkenhayn.

Falkenhayn's failure at Verdun had led to his replacement by Hindenburg and he was appointed to command the German Ninth Army, assembling in Galicia.

The Central Powers’ plan was obvious enough. There would be an attack on the Romanians in Transylvania, combined with an attack along the Black Sea coast into the Dobrudja province – fertile lands, inhabited mainly by Bulgarians and taken from Bulgaria in 1913, which the Bulgarians were keen to recover.

The Romanians did not expect the attack in the South. First, they thought that the Western Powers forces in Salonika would pin down most of the Bulgarian army. This was not the case. The attack from Salonika was a complete failure, and did not prevent Germans, Turks and Bulgarians from concentrating a substantial force against southern Romania. The Romanians had also expected Bulgaria to be deterred by the presence of a Russian force, Zayonchkovski’s, in the Dobrudja. In theory, the Bulgarians were Russophile; some even thought they might make peace once Romania entered the war on Russia’s side. This again was not the case.

The Western Powers had enough on their hands and could not contain Bulgarians; in any case, their Greek allies were of such doubtful allegiance that an entire Greek army corps refused to fight at all, surrendered in toto and was interned in Silesia for the rest of the war.

The Bulgarians hesitated about intervening; they even protested when German and Austro-Hungarian units stationed in Bulgaria took action against Romania, by bombing Bucharest, for instance. But they decided in the end to declare war on Romania, a day or so after their allies. In this way, a joint offensive of all four Central Powers became possible.

Bulgaria declared war on Romania, and a mixed force under Mackensen immediately invaded Dobrudja. The Romanian fortress at Turtucaia fell after only a day of fighting. With it the way was open for the Central Powers to move forward, sweeping the Romanian division aside, reducing the 1st Serbian and 61st Russian divisions to 3,000 men each, and forcing them out.

Von Mackensen, the elderly German commander in the Balkans, attacked out of Bulgaria almost immediately. Although most of the border between the two countries was the Danube, about four fifths of the way along the frontier, the river makes an abrupt turn to the north, leaving a wedge-shaped section of Romania with an ordinary land frontier. This was the country’s most vulnerable spot, because the Danube delta in the north meant that the only serious deep-sea port, then and now, is at Constantza, in the vulnerable section to the east and south of the river.

The Romanians were aware of their vulnerabilities, and at key points had built fortifications to block any offensive. The Romanian commander alleged to the press that Turtucaia, one of these forts, would be Romania’s Verdun. A day later the fort had fallen, with hardly a shot being fired, and von Mackensen’s patched-together army was spreading out into Romania. The Romanian plan had completely collapsed in only ten days.

Mackensen decided on a diversionary move against the Romanian fortress. A besieging force, actually smaller than the garrison, moved up. After the fortress fell, eighty percent of the garrison surrendered and the rest fled, their commander in the lead.

This, of course, was not supposed to happen. Maurice Sarrail’s army in the south was supposed to stop the Bulgarians from doing precisely this by attacking on their own. General Sarrail was the French commander in the Argonne whose offensives the Germans had repeatedly finessed by attacking first. Joffre claimed he was absolutely incompetent, and sacked him. But Sarrail had a sizeable following in the Chamber and was packed off to the Balkans. There he proved that Joffre did have an insight into the problems of command.

Silistra also had fallen, this time without even spoken resistance. The Bulgarians and their allies crossed the border and invaded Dobrudja. Here they were due to encounter Russian forces. But the collaboration of Russians and Romanians almost constituted an object-lesson in how not to run a multinational force. General Andrei Zaionchkovsky, though doing his best to maintain polite forms, complained again and again to Alexeyev that his task was impossible: to make the Romanian army fight a modern war was asking a donkey to perform a minuet. It did not help matters when Russian troops started looting from the local population.

The Romanians, at their allies’ mercy, could only exaggerate the Central Powers’ strength in the hope that more Russian troops would somehow be sent to save them. But Alexeyev was adamant: he felt that Wallachia and Dobrudja should be given up, and the Romanian army withdrawn into the Moldavian mountains until it had absorbed the facts of modern war.

Ordinary Russian soldiers regarded their allies with the utmost contempt, not least when these allies surrendered to Russian units, mistaking them for Bulgarian ones.

Russians sacked the countryside in a dress-rehearsal for the agrarian atrocities of 1917: estates laid to waste, wine cellars ruthlessly plundered, beasts’ throats cut, drunken soldiery drowned or boiled to death in vats of burning spirit.

Faced with an invasion from the south, and the potential loss of their only sea port, the Romanians had to make some hard choices: put everything into an attack into Transylvania, or try to eject von Mackensen from Dobrudja. Although the actual decision is usually thought of as wrong, it’s difficult to see what real options the Romanians had at this point. So they tried to mount operations in both directions, a plan for which they lacked the necessary resources.

From the Romanian point of view, things had gone disastrously wrong from the start. But to France and Great Britain, the Romanian campaign looked more promising. The German and Austrian General Staffs were going to have to send troops to Transylvania. If the Entente analysis of casualties was correct, diversion of the forces needed would cause the Western Front to collapse. Confident, the French and British pounded away on the Somme: the only way the Germans could ship men East was to pull them from the West.

Romania was virtually indefensible. The richest part of the country, Wallachia, jutted out in a long tongue between Hungary and Bulgaria: neither the Carpathians — traversed by many passes — nor the Danube offered real obstacles to an invasion. Yet the Romanians could not simply abandon Wallachia, since this would mean loss of their capital.

Threats to Dobrudja compelled the Romanian High Command to think again. A Crown Council in Bucharest determined that operations in Transylvania should be suspended, to permit the transfer of half of the army against Bulgaria. A ‘Southern Army Group’ would be assembled under General Alexandru Averescu to cross the Danube into Bulgaria. Meanwhile, Zayonchkovski’s Russo-Romanian force would contribute an offensive against the Bulgarians who had arrived in Dobrudja.

The new plans would soon become irrelevant. A real enough superiority was gradually built up: 195 battalions, 55 squadrons and 169 batteries to 110, 28 and 72 on the Central Powers’ side.

In an effort to stop the Central Powers advance in southern Romania, an attack was to be made between Zimnicea and Flămânda. The goal was for the Romanians to cross the Danube and attack enemy positions there. It was a burlesque. The Flămânda enterprise had to be abandoned because this strategic maneuver had been achieved at the cost of Romanian positions in Transylvania. In Dobrudja, things took a similar course, with the complication that Romanians misunderstood Russian orders, and in any case were not keen on obeying them.

Bridges were inadequate and broke down under the weight of guns and horses. Austro-Hungarian gunboats did much damage to the infantry as it tried to cross. Boats leaked. Such initial success as the crossings had was owing almost entirely to the deduction made by the local German commander, from the Romanians’ behavior, that they were only there to defend Bucharest.

Von Falkenhayn, the new theater commander, arrived in Transylvania bringing with him the nucleus of a sizeable Austro-German force, subsequently known as the Ninth Army. He was as little hindered as Mackensen. By the end of October Falkenhayn had forced the Romanian troops to retreat from Transylvania by his win at Kronstadt, today known as Brașov. Despite assurances of the British High Command in London that the Carpathians were impassable if defended, by the middle of November the Germans had broken through the passes and were in the Romanian plains heading toward the capital, Bucharest.

The railways that fed reserves to Transylvania were superior to anything on the Romanian side. By the third week of September, the Central Powers’ forces had been stepped up to 200,000 men, half of them German. The Kowel offensive did almost nothing to prevent this.

The Romanians’ advance had been of the worst possible kind. It had brought them beyond their own lines of supply, but it had not brought them forward to any point where they could disrupt the arrival by rail of the Central Powers troops.

Falkenhayn, whose troops included the formidable mountain division known as the Alpenkorps, in which the young Erwin Rommel was serving, made his move in Transylvania and began to push the Romanians back through the passes toward the central plain and the capital, Bucharest.

For ten days Falkenhayn rolled the Romanians back toward General Platon Lechitsky's Russian troops. Near Vatra Dornei, six Romanian battalions decamped. Lechitsky plugged the gap temporarily with two cavalry divisions, but the Ninth Army had to take over the empty sector or its flank would be turned.

The various Romanian groups stood in isolated blocks just north of the Carpathians: usually in utter ignorance as to each other’s whereabouts, and with no possibility of establishing rapid contact in battle. Falkenhayn drove against one of these isolated corps, at Hermannstadt, and pushed it back through the Turnu Roşu pass. The Romanian corps to its right, near Kronstadt, did not learn anything of this, and was itself driven back with much loss over the mountains.

Transylvania was once more virtually completely in the hands of the Central Powers. Now Falkenhayn could cross the mountains into Wallachia and join up with Mackensen’s forces on the Danube. To avoid this, the Romanians decided to take back from the Danube the troops they had sent in the second half of September. In the short term, this succeeded. The passes into Wallachia were blocked, and throughout October Falkenhayn’s groups had a difficult time, pushing through the snow from one defense-position to another on their way through the mountains.

From time to time, Conrad von Hötzendorf, the Austrian Chief of Staff, suggested more ambitious plans: a great offensive toward Bucharest, from the passes just to the northwest of it. This plan made too little sense on the ground for it to be adopted. Throughout October, the Central Powers’ action here was more important for the troops that it pinned than for the ground it gained.

On the southern front, the Central Powers offensive achieved considerable results. An offensive into Dobrudja was prepared and launched, mainly with Bulgarian and Arab divisions. Zayonchkovski’s army had not been strengthened. Defense of the Dobrudja province was another piece of burlesque. Bombardment struck the Romanians on the right, who retired without informing the Russians in the center. In no time, the railway line between Cernavoda and Constantza, the main Romanian port, was broken. Constantza itself was not defended.

Zayonchkovski complained that his force was ‘only the bone thrown to the Romanians to get them into this war’; he went on at length about the ‘repulsive impression as regards military matters’ that he had gained of his allies, and about their ‘utter misunderstanding of modern war, their appalling inclination to panic’. But Stavka merely answered that, since the Romanians were not in any position of numerical inferiority, there should be no complaints.

The Russian center fell back in confusion, and the race to retreat was then won by the Romanian left, which fled back along the Black Sea coast, pursued by Bulgarian cavalry over the sands.

The Russians had ordered Constantza to be destroyed, but the Romanians regarded it with too great pride to let this happen, and no doubt felt that their allies would make a thorough job of the destruction, if allowed to do so. They therefore surrendered the port, intact and with huge stocks of grain and oil, before the Russians could knock it about. The Russian naval detachment supposedly guarding it then sailed away, leaving the Romanian defenders to their fate.

By the end of October, the Central Powers had captured more or less the whole of Dobrudja, and threatened to cut off Bucharest from the sea. The Romanians had to retreat from Dobrudja.

Alexeyev now began to recognize that he would have to do something. Elsewhere on the front the Kowel offensives had failed, and attacks in eastern Galicia were also dying down in failure; now the Central Powers had almost reached the Danube delta, and seemed to threaten southern Russia. Stavka first sent VIII Army to the Dniester, and then agreed to send another army to constitute, ‘Army of the Danube’ with a view to the defense of the delta and Galați. Finally, IV Army was earmarked for Romania. In the end the Russian armies would arrive too late for Romania’s capital, Bucharest.

Throughout November, a great movement of Russian troops was under way. But the railway lines could take only 200 waggons a day, at a time when supply alone needed 433. The management of these lines was such that a French railway expert suffered a nervous breakdown when he was detailed to sort them out. It was not until mid-December that the Russian troops arrived in full strength, and even then they were badly under-supplied. Early in November, what arrived could suffice only to prevent further Bulgarian progress along the Black Sea coast.

This maneuver of Russian troops could not change things in Wallachia. The Russian troops could not reach Bucharest in time, nor indeed did Alexeyev particularly want them to, for he was concerned only with defending Moldavia and the approaches to southern Russia.

Early in November, German troops penetrated the passes into the western part of Wallachia — Oltenia — and by mid-November had reached the plains. A cavalry corps moved east towards Bucharest, dislodging the defenders from the southern parts of other passes. The German-Bulgarian force crossed the Danube, and found the task easy enough, since the Romanians had now diverted most of their forces back to the Carpathian front. By the end of November the two armies of the Central Powers were threatening Bucharest.

For the defense of Bucharest, the Russians had sent only a cavalry corps, but it was exhausted in covering 400 miles. Even re-shoeing the horses could take up to a week in Romanian conditions.

There was a final episode of drama. The Romanians had now been sent a French military mission, under Henri Berthelot, Joffre’s chief of staff during the battle of the Marne. He had visions of a Balkan Marne: a flank-attack on the Germans as they approached Bucharest, crossing the Argeș river. Berthelot built up a masse de manoeuvre: divisions scraped from the Danube and the Carpathians. The Romanian soldiers were driven forward into an affair that only consumed what was left of the reserve divisions. The Germans repelled ‘the Romanian Marne’ easily enough.

Berthelot was full of fight; he wished to build up the Romanian army — so much so that Stavka found his talk dangerous, and requested his removal.

Mackensen's army had crossed the Danube and was approaching Bucharest. The Romanian capital promptly fell into German hands. Assailed on three sides by four enemies, for the Turks had sent two divisions by sea to Dobrudja, the Romanians had been thrown into full retreat toward their remote eastern province of Moldavia, between the Siret River and the Russian border. There, as winter closed in, and with support from the Russians, they entrenched themselves on the Siret to sit out the bad weather.

British military representatives prudently toured the oil-areas of Ploiesti, setting light to the wells. In clouds of smoke, the remnants of the Romanian divisions withdrew to the north, leaving Bucharest to Mackensen who entered the Romanian capital triumphantly.

The remnants of Romania’s armies and government were penned up behind the Siret, in Moldavia. The only city of any size still remaining in their hands was Jassy, the cradle of that peculiarly Romanian blend of religious nationalism and anti-Semitism which would so disfigure the country’s psyche postwar.

The Russian South-West Front's mission was no longer to eliminate Austro-Hungary, but to prevent Romania's complete collapse. The onset of winter brought little relief. Defense of the Romanian front became Stavka's main preoccupation because failure could open the way into Ukraine and the Russian rear. All offensive plans were scrapped.

The extension of the Russian Ninth Army's front meant an additional army was needed. The Eighth Army's Staff was transferred in mid-October from Lutsk to Czemowitz, the Ninth's front was divided in two, and most of its troops were allocated to the new Eighth Army. The Dobrudja Detachment grew to ten divisions and became the 'Danube Army'.

The North and West Fronts would undertake only minor operations, and many of their units would be sent to the new Romanian Front, formed from the Danube Army and the remnants of four Romanian armies. This was nominally commanded by the Romanian King Ferdinand, but really by General Vladimir Sakharov.

After the fall of Bucharest, Romanian and Russian pleas to the French to activate the expeditionary force at Salonika against Bulgaria produced no significant results. The Western Powers pronounced Romania solely Russia's responsibility; and extension of the front line by about 250 miles (400 km) to the Black Sea coast forced Russia to provide 55 infantry and 15 cavalry divisions to man it.

The Russians now abandoned the Brusilov method that had brought such remarkable results: they returned to the old system of attacking a narrow front in a predictable way with a huge phalanx. The Brusilov method could succeed, in the first place, only if new troops were constantly fed to the front. But this would depend on the generosity of the other army group commanders, who effectively controlled the reserves. The problem was that they had no confidence in Brusilov’s methods, since they did not understand them.

Of the twenty-three Romanian divisions, six had ‘disintegrated’, two had been ‘captured’, and the rest contained, together, 70,000 men. Mackensen plodded after them. But with the arrival of Russian troops, the Germans’ progress was slow. They were held up at Urziceni, and then, in a battle over Christmas, at Rîmnicu-Sarat. By early January, they were lodged on the Siret, on the border of Moldavia, and could not progress beyond bridgeheads.

On the Russo-Romanian side, there was also little appetite for action. The Romanian army had been put to flight; it could count on a manpower reserve of less than 250,000 men, most of them quite untrained. The Russians, who now dominated the area completely, had no stomach for further offensive action. Their only action of any scale between early January and the Kerensky offensive of midsummer was a stroke on the Baltic coast.

Early in January 1917 the Russians profited from the withdrawal of German troops to stage a coup in Courland. They attacked by surprise, in an area of sand-dunes that masked the attackers’ activity; did not bombard in advance; did not attack in ‘waves’. In return for a few thousand casualties, they won a respectable success: thirty-six German guns and 8,000 prisoners. It was a symbol of the patterns prevailing on the eastern front. Minor attacks, launched by surprise, generally achieved far more impressive results than major ones preceded by heavy bombardment.

The Central Powers conquered the country easily enough, and, in the next year and a half, removed far more from it than they could have done had it remained neutral: over a million tons of oil, over two million tons of grain, 200,000 tons of timber, 100,000 head of cattle, 200,000 goats and pigs, over and above the quantities requisitioned for maintenance of the armies of occupation. Romanian intervention, in other words, made possible the Germans’ continuation of the war into 1918. The essential reason for this, aside from the obvious boost of resources, was the Central Powers’ capacity to shift their reserves quickly.

In the First World War, it was the great profusion of reserves that counted most. Contrary to legend, it was not so much the difficulty, or physical impossibility, of breaking through trench-lines that led to the war’s being such a protracted and bloody affair, but rather the fact that even a badly-defeated army could rely on reserves, moving in by railway. The conscription of whole generations, and particularly the enlarged capacity to supply millions of soldiers, meant that man-power was, to all intents and purposes, inexhaustible: even the total casualties of this war were a small proportion of the available man-power.

Alexeyev, in a rare flash of realism, actively discounted the value of the Romanians as allies, rightly reckoning that they would drain rather than add to Russian reserves. He certainly did little to assist them. Nor did the French and British at Salonika, whose undertaking to mount a diversionary offensive had been a major consideration in bringing Romania to declare war. However, that does not excuse the Romanians’ entry into a war for which they were ill-equipped and ill-prepared. Their decision for war had been disastrous. They had lost 310,000 men - nearly half as prisoners - and almost the whole of their country.

The Entente’s decision to entice Romania into the war had also been ill-judged. The addition of the nominal fighting power of lesser states - Portugal, Romania and even Italy - did not enhance the strength of the Entente but, on the contrary, diminished it, once the inevitable setbacks they underwent came to require the diversion of resources to shore them up.

The defeat of Romania not only necessitated, as Alexeyev had foreseen, the commitment of the Russian armies to rescue them from total collapse, it also delivered into German hands, over the next eighteen months, a million tons of oil and two million tons of grain, the resources that ‘made possible the ... continuation of the war into 1918’.

There was hardly any Romanian Army left by January 1917. Nor was much left to arm them with: the invading armies claimed they had captured 350,000 rifles and 350 pieces of artillery. Where would this new Romanian Army come from? ‘Free’ Romania was now a small piece of Moldavia.

When the Romanians intervened, the Central Powers’ system for pooling reserves worked equally well: the Romanian offensive was stopped in its tracks, as all four Central Powers mustered substantial forces against Romania almost at once.