In the Baltic states, the term partisans was not used for armed resistance fighters because of the politicised meaning of the word during the Soviet era. In Estonian, the metsavennad, in Latvian mežabrāļi and in Lithuanian miško broliai, were units operating in Estonia, Latvia and Lithuania during the Second World War and later after the Soviet invasion, which continued the struggle against Soviet rule.
In 1940, the Soviet Union occupied and annexed Estonia, Latvia and Lithuania. Due to the threat of repression, former state figures, military personnel and other socially active or prominent people were hidden in the forests. In particular, the number of forest brothers increased after the mass deportation on 14 June 1941.
During the German occupation, the Forest Brothers formed the Self-Defence Forces.
The Red Army reconquered Estonia, Latvia and Lithuania in 1944-1945. In the following years, more than 70,000 Baltic citizens hid in the forests due to Stalinist repression and Soviet rule. The size and composition of the resistance units ranged from forest brothers armed solely in self-defence to large and well-organised combat-ready groups.
In the late 1940s and early 1950s, the British (MI6), American and Swedish intelligence services provided the Forest Brothers with equipment, communications and logistical information. Such assistance played a key role in guiding the Baltic resistance movement, although it declined significantly after a serious compromise regarding MI6's Operation Jungle, when British double agents (Kim Philby and others) passed information to Soviet authorities, allowing the KGB to identify, infiltrate and dismantle many Baltic partisan units and prevent them from any further exposure to Western intelligence.