Spain's King Carlos III, in an effort to put more of the revenues in his own pocket, slashed the colonial nobles' share of the mining wealth. Then, in another financially-driven decision, he expelled the entire Jesuit community from all Spanish colonies, replacing them instead with Franciscan missionaries. These two actions in such rapid succession - 1765 and 1767, respectively - both infuriated and alienated pretty much everyone, as classes ranging from poor laborers to wealthy barons were loyal to the Jesuits.
"Criollos" (Mexican-born Spaniards) throughout the states of Guanajuato and neighboring Querétero starting getting pretty fed up with the power of Spanish-born colonists. In 1810, lawyers, businessmen, military figures and other members of the Criollo class began to meet under the guise of "literary societies," when they outlined plans for a rebellion. Across the ocean, Spain was suffering from political troubles due to the widespread occupation of Napoleon Bonaparte, which led to political confusion throughout its Spanish colonies. The opportunity to strike was there.
Enter Miguel Hidalgo.
Continue: Miguel Hidalgo & Mexican Independence