As a result of the war of 1808-1809, Sweden surrendered Finland to Russia. Finland became an autonomous grand duchy with the czar assuming the title Grand Duke of Finland. There were strong attempts at times to "Russianize" Finland, causing a growing desire for complete independence. Following the Russian Revolution in 1917, Finland declared its independence. Civil war broke out in 1918, with Soviet-supported communist troops fighting German-supported non-communists. In 1920 a peace treaty was signed with the USSR following a territorial war over Karelia, although relations between the two countries remained cool.