What were some political causes of the Mexican War of Independence?

The major reasons behind the Mexican War of Independence have their roots in the social struggle for freedom from Spanish rule. However, there were some important underlying political catalysts for the war as well. To understand the political causes of the revolution in Mexico, it is important to consider the political situation in Spain in the early 19th Century.
In 1808, Joseph Bonaparte was installed as the King of Spain by his brother Napoleon not long after the French invasion. He was very much unliked by the majority of the Spanish populace. His mere presence as king instigated a revolt against his rule known as the Peninsular War. Spanish nationalists fought to return Spain to Spanish rule and expel the French from political control of their country.
The Mexican elite were also divided over loyalty to the new monarch in Spain and the old system of Spanish kings. Supporters of Spanish rule were successful in ousting the viceroy of Mexico and installing Pedro Garibay, a retired Spanish general, to the position. All this led to a very uncertain political situation in Mexico.
While Spain was consumed by its struggle in Europe and Mexican political control was itself very uncertain, Mexican proponents of independence sensed that this would be an opportune time make their bid for liberty. On September 16, 1810, Miguel Hidalgo made his famous cry for freedom that officially began the Mexican War for Independence.
http://coursesite.uhcl.edu/HSH/Whitec/xhist/MexIndWar.htm