On the eve of outbreak of World War I, IMRO paramilitary activity in Serbia aimed to provoke a war with Bulgaria. At that time Serbia implemented in Macedonia a program of forced Serbianization. In an incident during 1914, when Bulgaria was still neutral, ca. 2,000 strong IMRO-cheta attacked a railway bridge over the Vardar River, massacring 477 men. In another incident in the same year, the first Macedonian recruits mobilized into the Serbian army demonstratively refused to take the military oath in Kragujevac, and were subjected to repression. As result IMRO set up a secret committee in Veles, which aim was to coordinate the transfer to Bulgaria of thousands of Macedonian deserters by the Serbian army. Later its comitadjis were incorporated into the regular Bulgarian Army and its power grew in significance. The fact that these paramilitary companies joined the Bulgarian Army marked a significant change in the way they were conducting war. At the beginning it formed the 11th Macedonian Infantry Division, and later other units, as for example "guerilla companies". Its entrance into the war towards the end of 1915 contributed to the defeat and occupation of Serbia, and the unification of Macedonia with Bulgaria. In Serbia the IMRO activity was identical with the Bulgarian policy, supporting the Bulgarization of the area. At the end of 1915 and the beginning of 1916 several massacres of (sic) "Serbomans" were conducted in Vardar Macedonia in the areas of Azot, Skopska Crna Gora and Poreče by IMRO-irregulars, aided by the guerrilla companies of the 11th Macedonian Infantry Division. The police chief of the Military Inspection Area of Macedonia reported to the interior minister that he cannot deal with the lawlessness of the paramilitaries. In fact 1917 was the turning point when IMRO became the instrument used by the Bulgarian government to gain control over the internal situation in the Pomoravlje and most from the region of Macedonia. At that time the IMRO leaders as general Aleksandar Protogerov headed the Bulgarian occupation troops in Morava region and crushed the uprising in the Toplica district with the help by IMRO irregulars. Their methods caused death of thousand people, destruction of their property, looting and other war crimes committed during the war in the parts of the Kingdom of Serbia under Bulgarian control.