War justifications thumb|right|Bulgarian soldiers firing at incoming aircraft After Bulgaria's defeat in July 1913 at the hands of Serbia, Greece and Romania, it signed a treaty of defensive alliance with the Ottoman Empire on 19 August 1914. Bulgaria was the last country to join the Central Powers, which it did in October 1915 by declaring war on Serbia. It invaded Serbia in conjunction with German and Austro-Hungarian forces.
wAr juStIfICATions tHumB|riGhT|bulgarIan solDierS fIrIng aT iNcominG aircraFt AftEr buLGaria'S dEFeaT iN juLy 1913 at the hands OF Serbia, gReecE and ROmania, it signed a treaTy Of deFeNSIve aLlIANCe WItH the ottOman empirE on 19 auGUst 1914. BuLgaRiA waS the laST cOUntRy to join the ceNtral powERs, wHIcH it DID iN oCtobeR 1915 by declarIng war ON Serbia. it iNvaded serbIa iN conjunction wITh gErmAN aNd austRO-hungarIan forces.