Before the outbreak of the Second World War, Germany and the Soviet Union signed the German-Soviet Nonaggression Pact, concerning the partition and disposition of sovereign states, including Estonia. In particular its of August 1939.
The Republic of Estonia declared neutrality in the war but fell under the Soviet sphere of influence due to the Molotov–Ribbentrop Pact and was occupied by the Soviet Union in 1940. Mass political arrests, deportations, and executions followed. In the Summer War during the German Operation Barbarossa in 1941, the pro-independence Forest Brothers captured South Estonia from the NKVD and the 8th Army before the arrival of the German 18th Army. At the same time, the Soviet paramilitary destruction battalions carried out punitive operations, including looting and killing, based on the tactics of scorched earth proclaimed by Joseph Stalin. Estonia was occupied by Germany and incorporated into Reichskommissariat Ostland.
In 1941, Estonians were conscripted into the 8th Estonian Rifle Corps and in 1941–1944 to the Nazi German forces. Men who avoided these mobilisations, fled to Finland to be formed into the Finnish Infantry Regiment 200. About 40% of the Estonian pre-war fleet was requisitioned by British authorities and used in Atlantic convoys. Approximately 1000 Estonian sailors served in the British Merchant Navy, 200 of them as officers. A small number of Estonians served in the Royal Air Force, in the British Army and in the U.S. Army.