The territory of Estonia has been inhabited since at least 9,000 BC. Ancient Estonians became some of the last European pagans to adopt Christianity following the Livonian Crusade in the 13th century. After centuries of successive rule by Germans, Danes, Swedes, Poles and Russians, a distinct Estonian national identity began to emerge in the 19th and early 20th centuries. This culminated in independence from Russia in 1920 after a brief War of Independence at the end of World War I, where Estonians, led by General Laidoner, had to fight for their newborn freedom. Initially democratic prior to the Great Depression, Estonia experienced authoritarian rule from 1934 during the Era of Silence. During World War II, Estonia was repeatedly contested and occupied by Germany and the Soviet Union, ultimately being incorporated into the latter as the Estonian SSR. After the loss of its "de facto" independence to the Soviet Union, Estonia's "de jure" state continuity was preserved by diplomatic representatives and the government-in-exile. In 1987, after the peaceful Singing Revolution, its "de facto" independence was restored on 20 August 1991.