Finland was terrified of a repeat of the Winter War of 1939-1940. It was a military conflict between the Soviet Union and Finland in 1939–1940. It began with the Soviet invasion of Finland on 30 November 1939, and ended with the Moscow Peace Treaty on 13 March 1940. Finland joined forces Nazi Germany in 1941 as a bid to regain lost territory like Petsamo, only to find it's self on the losing side. Finnish–Estonian defence cooperation was the mainstay of defence Estonia's plans in the 1930s and 1990s.