Timeline By Josue.S 1808 Napoleonic invasion of Spain; weakens Spanish control over its colonies. 1810 Cry of Dolores (September 16); beginning of the Mexican War of Independence. 1811 Battle of Calderón Bridge; insurgents are defeated. 1814 Constitution of Apatzingán; first attempt at insurgent governance. 1815 Vicente Guerrero emerges as a key insurgent leader in the south. 1820 Liberal revolution in Spain; influences independence negotiations. 1821 Plan of Iguala; establishes the basis for independence. 1821 Treaty of Córdoba (August 24); confirms Mexico’s independence. 1821 Army of the Three Guarantees enters Mexico City (September 27). 1822 Agustín de Iturbide is proclaimed emperor. 1823 Iturbide abdicates; collapse of the First Mexican Empire. 1824 Federal Constitution establishes Mexico as a republic. 1833 Tensions between federalists and centralists intensify. 1835 Texas Revolution begins. 1836 Texas declares independence (March 2); Texan victory at San Jacinto (April 21). 1845 U.S. annexes Texas, increasing tensions with Mexico. 1846 Mexican-American War begins (April 25). 1848 Treaty of Guadalupe Hidalgo (February 2); Mexico cedes territory to the U.S.