In spite of some reverses against the Latin Empire in 1240, John III was able to take advantage of Ivan Asen II's death in 1241 to impose his own suzerainty over Thessalonica (in 1242), and later to annex this city, as well as much of Bulgarian Thrace in 1246. Immediately afterwards, John III was able to establish an effective stranglehold on Constantinople in 1247. In the last years of his reign Nicaean authority extended far to the west, where John III attempted to contain the expansion of Epirus. Michael's allies Golem of Kruja and Theodore Petraliphas defected to John III in 1252.