During the period between the Winter War and the German invasion of the Soviet Union in 1941, there were disputes between Finland and the Soviet Union over mining rights in Petsamo. Finland refused to allow the Soviet Union to mine nickel in Petsamo. This was one of the causes of hostility between the Soviet Union and Finland, which led to the Continuation War. As part of the German invasion, troops from Norway occupied the Petsamo region in 1941, securing the nickel supply.