Bayan yakin Balkan , ra'ayin Bulgarian ya juya zuwa ga Rasha da kuma Yammacin Turai, wanda Bulgarians suka ji cin amana.Gwamnatin Vasil Radoslavov ta haɗa Bulgaria da Daular Jamus da Ostiriya-Hungary, duk da cewa wannan yana nufin zama abokin Ottomans , maƙiyin gargajiya na Bulgaria.Amma Bulgaria a yanzu ba ta da wani da'awar a kan Ottomans, yayin da Serbia, Girka da Romania (kawancen Birtaniya da Faransa ) ke da ƙasashen da aka gane a Bulgaria a matsayin Bulgarian.Bulgaria ta zauna a shekara ta farko na yakin duniya na farko na murmurewa daga yakin Balkan.^[43] Jamus da Ostiriya sun fahimci cewa suna buƙatar taimakon Bulgaria don cin nasara kan Serbia ta hanyar soja ta yadda za a bude layin samar da kayayyaki daga Jamus zuwa Turkiyya da kuma karfafa Gabashin Gabas da Rasha.Bulgeriya ta dage kan samun manyan ribar yankuna, musamman Masedoniya, wanda Ostiriya ba ta son ba da ita har sai da Berlin ta dage.Bulgaria kuma ta yi shawarwari tare da Allies, waɗanda suka ba da ɗan ƙaramin karimci.Tsar ya yanke shawarar tafiya tare da Jamus da Ostiriya kuma ya sanya hannu kan ƙawance tare da su a cikin Satumba 1915, tare da tsari na musamman na Bulgarian-Turkiyya.An yi hasashen cewa Bulgaria za ta mamaye yankin Balkan bayan yakin.^[44]Bulgariya, wadda ke da ƙarfin ƙasa a yankin Balkan, ta shelanta yaƙi a kan Serbia a watan Oktoba na shekara ta 1915. Biritaniya, Faransa daItaliya sun mayar da martani ta hanyar shelanta yaƙi a Bulgaria.A cikin kawance da Jamus, Ostiriya-Hungary da Ottomans, Bulgaria ta ci nasarar soja a kan Serbia da Romania, ta mamaye yawancin Macedonia (ta dauki Skopje a watan Oktoba), ta shiga Macedonia ta Girka, kuma ta dauki Dobruja daga Romania a watan Satumba 1916. Don haka Serbia ta kasance na dan lokaci. an fitar da kasar daga yakin, kuma an ceto Turkiyya na dan wani lokaci daga durkushewa.^[45] A shekara ta 1917, Bulgaria ta tattara fiye da kashi ɗaya bisa huɗu na al'ummarta miliyan 4.5 a cikin sojoji 1,200,000, ^[46] kuma ta yi asara mai yawa akan Serbia (Kaymakchalan), Burtaniya (Doiran), Faransa (Monastir), Rasha. Daular (Dobrich) da Masarautar Romania (Tutrakan).Duk da haka, ba da daɗewa ba yaƙin ya zama ruwan dare ga mafi yawan ’yan ƙasar Bulgeriya, waɗanda suka sha wahala mai yawa na tattalin arziki, kuma ba sa son yaƙar ’yan’uwansu Kiristocin Orthodox a ƙawance da Daular Usmaniyya.Juyin Juyin Juya Halin Rasha na watan Fabrairun 1917 ya yi tasiri sosai a Bulgeriya, inda ya yada kyamar yaki da sarautu tsakanin sojoji da birane.A watan Yuni gwamnatin Radoslavov ta yi murabus.An yi kisan gilla a cikin sojoji, an saki Stamboliyski kuma aka yi shelar jamhuriya.