The Mexican War/The War Against Iraq.
and Mexico was started because of a Mexican attack on American troops along the southern border of Texas on April 25, 1846. After Winfield Scott occupied Mexico City on September 14,1847, a few months later a peace treaty was signed between Mexico and the U.S.
A dictatorial Centralist government in Mexico began the war because of the U.S. annexation (1845) of Texas, which Mexico continued to claim despite the establishment of the independent republic of Texas 10 years before. Another possible cause for the war may be that the U.S. brought on the war by annexing Texas and, just to make Mexico angry, by stationing an army at the mouth of the Rio Grande.
During the war Mexico's government was very unstable because the federal constitution of 1824 had been abrogated in 1835 and replaced by a centralized dictatorship. Also the Federalists, who supported a constitutional democracy, and the Centralists, who were in control of the government from 1835 to December 1844, were opposed factions of each other. Numerous rebellions had occurred within Mexican territory and the Texas revolution had resulted in the independence of Texas. In December 1844 a coalition of moderates and Federalists forced the dictator Antonio Lopez de Santa Anna into exile and put Jose Joaquin Herrera as the acting president of Mexico but still other Centralists in favor of Santa Anna began planning to overthrow Herrera, and the U.S. annexation of Texas provided them with a perfect cause.
The annexation of Texas by the U.S. had also caused trouble within the United States. James Polk won the 1844 presidential election by advocating a belligerent stand against Britain on the Oregon Question. After he was in office, he declared, ". the people of this continent alone have the right to decide their own destiny." Also the term Manifest Destiny came into the picture to describe what was regarded as a God-given right to expand the U.