Background of the Mexican War

The Polk Administration, 1846-1848

The Mexican War was likely an unnecessary conflict with multiple causes, including the following:

• The decision of the Tyler administration in March, 1845 to annex Texas, then an independent republic, but still claimed by Mexico
• The stationing of U.S. soldiers near the Rio Grande on territory regarded by many as Mexican soil
• The Polk administration was an advocate of the country's Manifest Destiny, a belief that God had intended the nation to stretch across the entire continent; the Southwest and California were especially appealing targets; further, Southern slaveowners were enthusiastic about the possibility of adding additional slave states to the Union
• Some in the United States viewed Mexico as a weak nation and incapable of holding on to territory desired by other nations; Britain, a continuing rival of the United States, had been casting envious glances at various parts of Mexico
• Mexico had alienated many in Congress by its failure to settle debts owed to U.S. citizens
• An incautious Mexican nationalism led their government to underestimate American military might and resolve; the Mexicans were confident of victory and anticipated an early reoccupation of Texas.

Despite being inclined toward war, President Polk did attempt a diplomatic fix by sending the Slidell Mission to Mexico City. Diplomatic failure was followed quickly by hostilities and warfare developed on the following fronts:

• The Western Campaign
• The Taylor Campaign
• The Scott Campaign

Peace was achieved in the Treaty of Guadalupe Hidalgo and the results of the war had both immediate and long-term consequences.