In the summer of 1943, Boris died suddenly at age 49, leaving a three-man regency ruling for his six-year-old son, Simeon. Because two of the three regents were figureheads, Prime Minister Bogdan Filov, the third regent, became de facto head of state in this makeshift structure.

The events of 1943 also reversed the military fortunes of the Axis, causing the Bulgarian government to reassess its international position. Late in 1943, the Allies delivered the first of many disastrous air raids on Sofia. The heavy damage sent a clear message that Germany could not protect Bulgaria from Allied punishment. Once the war had finally intruded into Bulgarian territory, the winter of 1943-44 brought severe social and economic dislocation, hunger, and political instability. The antiwar factions, especially the communists, used urban guerrilla tactics and mass demonstrations to rebuild the organizational support lost during the government crackdown of 1941. Partisan activity, never as widespread as elsewhere in the Balkans during the war, increased in 1944 as the Red Army moved westward against the retreating Germans. To support antigovernment partisan groups, in 1942 the communists had established an umbrella Fatherland Front coalition backing complete neutrality, withdrawal from occupied territory, and full civil liberties.

Early in 1944, Bulgarian officials tried to achieve peace with the Allies and the Greek and Yugoslav governments-in-exile. Fearing the German forces that remained in Bulgaria, Filov could not simply surrender unconditionally; meanwhile, the Soviets threatened war if Bulgaria did not declare itself neutral and remove all German armaments from Bulgaria's Black Sea coast. Unable to gain the protection of the Allies, who had now bypassed Bulgaria in their strategic planning, Bulgaria was caught between onrushing Soviet forces and the last gambits of the retreating Nazis. At this point, the top priority of Bulgarian leaders was clearing the country of German occupiers while arranging a peace with the Allies that would deprive Soviet forces of an excuse to occupy Bulgaria. But in September 1944, the Soviet Union unexpectedly declared war on Bulgaria, just as the latter was about to withdraw from the Axis and declare war on Germany.

Data as of June 1992