August, 1846 - September, 1846
Conservative general Mariano Paredes had seized power in early January, 1846, and not long afterward instructed General Mariano Arista, commander of the Army of the North, to cross the Rio Grande and attack U.S. forces. But the nation had not rallied around the government during the crisis. Paredes maintained that the country could best be preserved by bringing back the Spanish monarchy, a position that alienated all but a handful of conservatives. A few weeks after U.S. and Mexican forces clashed on the Rio Grande, federalist revolts in opposition to Paredes flared in Jalisco and Guadalajara. The insurrection had spread to the capital by the end of July, prompting Paredes to hand the reins of government over to his vice president, General Nicholas Bravo, giving as his reasons the need to take command of the war effort. No sooner had he resigned, however, than the Mexican city garrison rebelled, issuing the Plan de La Ciudadela. One of the ringleaders, General José Mariano Salas, formed an interim government and reinstated the Constitution of 1824.
The collapse in quick succession of the federalist Herrera and conservative Paredes regimes had not gone unnoticed by Santa Anna, then living in exile in Havana, Cuba. Seeking to capitalize on the political discord, the disgraced Mexican leader had quietly begun to rebrand himself as a moderate who could hold Mexico's disparate political factions together in this time of national crisis. He had also presented himself in the role of peacemaker to Mexico's adversary. In June 1845 and again in February 1846, President Polk had been visited by Alexander Atocha, a confidant of the exiled leader, who informed him that Santa Anna was prepared to negotiate for the sale of Texas should he return to power in Mexico. A meeting in Havana in July between the exiled leader and an emissary of the president, Alexander Slidell Mackenzie (John Slidell's brother), convinced Polk of Santa Anna's sincerity. As a result of these secret meetings, the prodigal leader sailed from Havana to Vera Cruz in mid-August, passing unmolested through the U.S. naval blockade. But instead of entering into peace negotiations with the Polk administration, Santa Anna proceeded to raise an army with which to launch a counter-offensive against U.S. forces. Polk's secret diplomacy had succeeded only in aiding the return of Mexico's most capable and energetic leader.