At the outbreak of the Second World War Bulgaria was ruled by Tsar Boris III (1918–1943). Bulgaria entered World War II in 1941 as a member of the Axis alongside Germany, Italy and Japan but did not participate in Operation Barbarossa, the invasion of Russia in Jun 1941.
The sudden death of Boris III in mid-1943 pushed the country into political turmoil as the war turned against Germany, and the communist guerrilla movement gained momentum in the country. The government of Bogdan Filov subsequently failed to achieve peace with the Allies.
Bulgaria did not comply with Soviet demands to expel German forces from its territory, resulting in a declaration of war and an invasion by the USSR in September 1944. The communist-dominated Fatherland Front took power, ended participation in the Axis Alliance and joined the Allied side until the war ended. Bulgaria suffered little war damage and the Soviet Union demanded no reparations.
Michel 375 and 376 "Tsar Boris III"
Issued 10th Feb 1940. These stamps were printed photogravure and are perf K12¾.