Why did Pope Innocent III later support Frederick II for the imperial throne?

Pope Innocent III’s decision to support Frederick II for the imperial throne in 1211 was a strategic reversal driven by the betrayal of his previous candidate, Otto IV.1

Initially, Innocent III had supported Otto IV against the Hohenstaufen candidate, Philip of Swabia, because the papacy feared the power of the Hohenstaufen dynasty and sought to keep the Kingdom of Sicily separate from the Holy Roman Empire. However, after Philip of Swabia was murdered in 1208, Otto IV violated his previous agreements with the pope and threatened papal interests in Italy.2

Faced with this betrayal, Innocent III turned to his former ward, Frederick II—the son of Emperor Henry VI—as a new candidate. To mitigate the risk of a single ruler controlling both Sicily and the Empire, Innocent exacted a promise from Frederick to keep the two kingdoms separate, with Frederick’s son, Henry, designated to rule Sicily while Frederick became emperor. Although Innocent was forced to support Frederick against his better judgment, he used the dispute to assert the papacy's right to evaluate and approve imperial candidates in contested elections.12