The Soviet-Finnish War, also known as the Winter War, took place from November 1939 to March 1940. It began when the Soviet Union invaded Finland in an attempt to gain territory and secure its northwestern borders. Despite being outnumbered, the Finnish forces utilized their knowledge of the terrain and effective guerrilla tactics to resist the invasion. The war ended with the signing of the Moscow Peace Treaty in March 1940. Finland ceded approximately 9% of its territory to the Soviet Union, including parts of the Karelia region. The conflict highlighted Finland's resilience and had lasting effects on its military and foreign policy.