The Italian defeat at the hands of Greece forced dictator Benito Mussolini to ask his German ally, Adolf Hitler, for help. In Yugoslavia, a pro-Allied coup compelled the Germans to act against that country. The German war machine advanced quickly into Yugoslavia, crushing any resistance. In Greece, despite the efforts of the Greek and British armies, the northern line of defense was breached, and German troops then proceeded towards Athens. Greece and Yugoslavia remained under Axis occupation until 1944-45.
Prince Regent Paul of Yugoslavia joined the Axis and signed the Germany-Italy-Japan Tripartite Pact, causing outrage in Belgrade. Allied successes in Greece, Albania and Libya encouraged the eighteen-year-old Prince Peter II of Yugoslavia to declare himself of age and overthrow Paul the following night, assisted by the Special Operations Executive (SOE). Hitler was rendered incandescent with rage by this coup.
As ever, the military skills of the German General Staff proved capable of the new demands, and a new plan was swiftly drawn up to deal with both states. Hungary, Bulgaria and Italy would be expected to provide assistance, for which they would receive territorial rewards. The Croats and other ethnic groups in the region were encouraged to rebel against the Serb-dominated Yugoslav government. The German army included a large armored component within its overall deployment. The combined invasion of Yugoslavia and Greece would draw upon two German armies totalling 32 divisions.
The Yugoslav army was in no position to repel the German attack. Its small peacetime army of 150,000 men could be mobilized to approximately 1.4 million troops. But many of its conscripts were not in place when the Germans struck along the long Yugoslav border. Its equipment was also old and outdated.
Plans for the invasion of Yugoslavia were made to coincide with the attack on Greece. Just ten days into their new-found freedom, with only two-thirds of their thirty-three divisions mobilized, the Yugoslavs were subjected to a massive invasion from the north, east and southeast by over half a million Axis soldiers. It was a perfect example of German Staff work and efficiency. Zagreb fell on the fourth day, Belgrade on the sixth, Sarajevo on the ninth and Yugoslavia formally surrendered after eleven days, with King Peter and the Government escaping with only hours to spare.
The victors divided the stricken country among themselves. Germany annexed a large area in the north and held the old core of Serbia under military administration. The Italians received a substantial piece in the northwest, much of the coast, and an addition to their Albanian colony. A puppet state of Croatia was created which at one time Hitler thought to place under Hungarian influence, then agreed to put under Italian control, and eventually tried to have the Germans direct themselves. Hungary received a share in the northeast and Bulgaria in the south. Violence continued throughout the occupation as various resistance groups fought the occupation and, sometimes, among themselves.
The main German relief expedition for Italy was to attack Greece through Bulgaria from Romania. The weather in the mountains near the Greek-Bulgarian border made such an offensive impossible before the spring of 1941, and the Italians would have to hang on in Albania until then as best they could. Bringing up sufficient forces and equipment for such an operation would occupy the intervening months, since such forces had to be shipped across Hungary, built up in Romania, and then launched across Bulgaria into Greece.
The Italian attack on Greece with its quickly obvious setbacks appeared to offer the British an opportunity along with an obligation. The obligation was to try to provide some substance to the guarantee the British had given to Greece when Italy occupied Albania; the opportunity was the possibility of creating on the continent of Europe a Balkan front based in Greece and supplied from North Africa. And from that base, there might be the possibility of raids on the Romanian oil fields. Troops were thus diverted from North Africa to the Greek front.
The Greeks had fully committed themselves to the fighting in Albania. To the east of that front they held two major positions which could block a German advance from Bulgaria, but both were open to possible flanking moves through Yugoslavia. Moreover, the Greeks were defending forward in Macedonia up toward the Bulgarian frontier. Nevertheless, despite the hazards, the British agreed to the Greek defensive scheme.
German Panzers struck at Skopje in southern Yugoslavia and across the southern flank of the Yugoslav Army; their objective was to outflank Greek positions. The Germans broke the Greek Third Army after fierce fighting and flanked Greek defenses. Initial attacks on the Metaxas Line in northern Greece only achieved limited success. However, the German drive through Yugoslavia forced the British and Greeks to retreat. The German advance engulfed the Greek rear areas in Albania. As the Germans rapidly pursued fleeing Allied forces toward Thermopylae, Greek generals in Albania deposed their commander and sought terms that did not include the Italians.
The main axis of advance lay through the Monastir gap, which ran through the high mountains into Greece. Spring had not yet reached this region, and the Germans were forced to battle through snow and freezing temperatures. The Germans had to take the Klidi Pass, the main route into Greece. The SS troops faced Australians and New Zealanders of the British Expeditionary Force. German casualties mounted, but after two days of hard fighting the defenders were prised from their positions, and the Germans made their way into the heart of Greece. The Allied forces had to withdraw towards Thermopylae.
The German breakthrough towards central Greece spelled disaster for the Allies, and a conference was held in Athens to assess the situation, attended by King George and his Commander-in-Chief, General Alexandros Papagos, and the British generals, Archibald Wavell and Maitland Wilson. All parties agreed that the battle was lost and that the British Expeditionary Force should withdraw from Greece. From then on, the holding operations at Thermopylae and Thebes were conducted with the intention of gaining time for the British and Commonwealth forces to be evacuated to Crete and Egypt.
Given the Greek collapse, the British could not hold Thermopylae. Nevertheless, the defense of the pass slowed the German advance. As the Germans pushed past Thermopylae, they launched a paratrooper drop on the Corinth Canal to cut off the retreating British forces as well as to capture the canal intact to protect the Italian-Romanian oil link. However, the British crossed the canal before the attack and destroyed its bridges.
The Germans assembled makeshift boats and managed to cross the Gulf of Corinth at Patras. Reinforced by the 5th Panzer Division, they now began to advance into the Peloponnese. German soldiers marched into Athens.
The British position was becoming increasingly desperate, but most of the troops were able to retreat to the southern Peloponnese before the Germans cut them off. There they were evacuated by the Royal Navy, who managed to save just over 50,000 British, Australian and New Zealand servicemen. Only at Kalamata did the embarkation break down, leaving 7,000 troops stranded on the Greek shore. Most of the men were captured, although some managed to break out of the German encirclement, and with the aid of the local population evade capture.
Greece was to suffer fearfully under German occupation. In the first eighteen months, no fewer than 40,000 Greeks starved to death, and the population was reduced by some 300,000 in the course of the war. Olive oil became a major currency as inflation meant that a single loaf of bread could cost 2 million drachma. The Germans resorted to methods of violence to keep control, as when all the male inhabitants of Kalavryta in the northern Peloponnese – 696 people in twenty-five villages – were shot by the 117th Jager Division in reprisal for guerrilla actions.
With control of Crete the Germans could threaten the eastern Mediterranean, bomb Egypt and Libya and protect the Corinth Canal, through which much of Italy’s oil was transported. Operation Merkur (Mercury) was launched against three airfields on the north coast of the island. This occasion marked the first mainly airborne invasion in military history, as the Germans used Fallschirmjäger (paratrooper) troops to attack the island. After 13 days of fighting the Germans emerged victorious.
In the Balkans, German air superiority had played as significant a role as it had in the Blitzkrieg in Norway and Western Europe. The failure of the Allies was also due to the inability of the British to send to Greece the size of forces and the quantities of supplies which they had anticipated providing.