After Robert of Courtenay died in 1228, a new regency under John of Brienne was set up. After the disastrous Epirote defeat by the Bulgarians at the Battle of Klokotnitsa, the Epirote threat to the Latin Empire was removed, only to be replaced by Nicaea, which started acquiring territories in Greece. Emperor John III Doukas Vatatzes of Nicaea concluded an alliance with Bulgaria, which in 1235 resulted in a joint campaign against the Latin Empire, and an unsuccessful siege of Constantinople the same year. In 1237, Baldwin II attained majority and took over the reins of a much-diminished state. The empire's precarious situation forced him to travel often to Western Europe seeking aid, but largely without success. In order to raise funds, he was forced to resort to desperate means, from removing the lead roofs of the Great Palace and selling them, to handing over his only son, Philip, to Venetian merchants as a guarantee for a loan.