Augustin de Iturbide was able to declare independence from Spain while also proclaiming himself emperor in part because

Iturbide’s declaration combined independence with a monarchy, a form of government familiar to many Spanish colonists. Mexico had been ruled by the Spanish Crown, so a king or emperor seemed a recognizable alternative to colonial rule. Iturbide had not started the independence movement, and his family background or military service alone does not explain why an emperor seemed acceptable.

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