Vatatzes ya mutu a ranar 4 ga Nuwamba 1254. Yin amfani da rashin manyan sojojin Nicene, Michael ya shiga cikin Macedonia kuma ya sake mamaye yankunan da Vatatzes ya yi asara a 1246 ko 1247. Masanin tarihin Byzantine, George Akropolites, ya rubuta cewa mazauna wurin da ke magana da Bulgaria sun goyi bayan Michael's. mamayewa saboda suna so su girgiza "karkiya na masu jin wani harshe".Theodore II Laskaris, ya kaddamar da mamaya a farkon 1255. Lokacin da yake magana game da sabon yaki tsakanin Nicea da Bulgaria , Rubruck ya kwatanta Michael a matsayin "wani yaro ne kawai wanda ikonsa ya rushe" ta Mongols .Michael ba zai iya tsayayya da mamayewa ba kuma sojojin Nicene sun kama Stara Zagora.Tsananin yanayi ne kawai ya hana sojojin Theodore ci gaba da mamayewa.Sojojin Nice sun sake kai farmaki a cikin bazara kuma sun mamaye mafi yawan kagara a tsaunin Rhodope.Mika'ilu ya shiga yankin Turai na Daular Nicea a cikin bazara na shekara ta 1256. Ya yi wa Thrace hari a kusa da Konstantinoful, amma sojojin Nice sun ci sojojinsa na Cuman.Ya roki surukinsa da ya shiga tsakani don sulhu tsakanin Bulgaria da Nicea a watan Yuni.Theodore ya amince ya rattaba hannu kan yarjejeniyar zaman lafiya bayan Michael ya amince da asarar filayen da ya yi da’awar Bulgaria.Yarjejeniyar ta kayyade kogin Maritsa na sama a matsayin iyakar kasashen biyu.Yarjejeniyar zaman lafiya ta harzuka mutane da yawa (masu daraja) waɗanda suka yanke shawarar maye gurbin Michael tare da ɗan uwansa, Kaliman Asen.Kaliman da abokansa sun kai hari ga Tsar wanda ya mutu daga raunukansa a ƙarshen 1256 ko farkon 1257.