World War I was the first modern, industrialized slaughter and the first “total war” in which combatants and civilians alike were regarded as legitimate targets. An imperialist war that exploded the contradictions between the global empires, it had a profound effect in reshaping European politics. It brought both deep traumas, but also new openings.

This was true even within the socialist movement. The outbreak of war in 1914 blew open the mounting tensions within European Social Democracy, as some went along with the nationalist fervor while others vehemently opposed it. The Bolshevik leader Vladimir Lenin, urged socialists to seize the political opportunity and turn the imperialist conflict into a revolutionary civil war.

In Russia, this did indeed play out, with the February and October revolutions of 1917. Yet rather less well-known are the events in the tsardom of Bulgaria. A peripheral, overwhelmingly agrarian state, Bulgaria’s rulers had sought to use the war to fulfill their own territorial aspirations by joining in the larger conflict between the great powers. The result, however, was an explosion of social tensions.

Having just suffered two exhausting Balkan wars in 1912 and 1913, the prospect of a third conflict had been deeply unpopular among the Bulgarian population upon the outbreak of the war in 1914. The government, led by a coalition of three liberal parties, assured Bulgarians that plans for war mobilization merely sought to prepare for the unlikely event of an outside attack. Meanwhile, both the Allied and Central Powers enticed Bulgaria to fight on their side with promises of territorial gains in Macedonia, Romania and northern Greece. Bulgaria signed a treaty to join the Central Powers on August 24, 1915 and began mass mobilization, before declaring war against Serbia two months later. 600,000 men were drafted, but at the peak of the fighting almost 900,000 — one-fifth of the total population — were enlisted.