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.