拉丁帝国
The Latin Emperor of Constantinople, Robert I, died in January 1228. His brother Baldwin II succeeded him, but a regent was needed to rule the Latin Empire since Baldwin was ten years old. Ivan Asen II of Bulgaria was willing to accept the regency, but the barons of the Latin Empire suspected that he wanted to unite the Latin Empire with Bulgaria. They offered the imperial crown instead to John, an ally of the Holy See.