 The outbreak of the First World War and the collapse of the Russian Empire during the Russian Revolution and Russian Civil War of 1917 – 1920 gave Finland a window of opportunity ; on 6 December 1917 , the Senate of Finland declared the nation 's independence . The new Bolshevik Russian government was weak , and with the threat of civil war looming Soviet Russia recognized the new Finnish government just three weeks after the declaration of independence . Sovereignty was fully achieved in May 1918 after a short civil war and the expulsion of Bolshevik troops . 
