The wave of national self-determination which swept eastern Europe started with Bolshevik revolution in Russia, and Lenin’s declaration of the people's ‘general right of self-determination’. Finland promptly declared independence in December 1917, which Soviet Russia confirmed. After declaring independence in 1918, Estonia and Latvia had to fight both Baltic Germans and Soviet Russia to confirm their nationhood. Poland warred with Soviet Russia, Lithuania and Czechoslovakia before its boundaries were established at the 1921 Treaty of Riga. The kingdoms of Austria, Hungary and Bulgaria, representing the defeated side in the war, were left much reduced by the Treaty of Versailles which, in addition, forbade any future union between Austria and Germany. The kingdom of Serbs, Croats and Slovenes united southern Slavic populations, while Romania was rewarded for its support of the Allies (and its 1919 Hungarian invasion) with the acquisition of Transylvania from Hungary, Bessarabia from Russia and Dobruja from Bulgaria.