The resulting political unrest led to the establishment of a royal authoritarian dictatorship by Tsar Boris III (1918–1943). Bulgaria entered World War II in 1941 as a member of the Axis but declined to participate in Operation Barbarossa and saved its Jewish population from deportation to concentration camps. 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. 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 and joined the Allied side until the war ended. Bulgaria suffered little war damage and the Soviet Union demanded no reparations. But all wartime territorial gains, with the notable exception of Southern Dobrudzha, were lost.