The Mexican-American War (1846-1848) was a pivotal conflict in U.S. history, and several factors contributed to its outbreak. Here are four key causes:
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Manifest Destiny: The belief in Manifest Destiny, the idea that Americans were destined to expand across the continent, fueled the desire for territorial expansion. Many Americans felt it was their right to spread democracy and civilization from the Atlantic to the Pacific, leading to tensions with Mexico over the annexation of Texas and further expansion into Mexican territories.
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Annexation of Texas: Texas, which gained its independence from Mexico in 1836, was annexed by the United States in 1845. This move was deeply resented by Mexico, which considered Texas a part of its territory. The annexation heightened tensions between the two nations and is often seen as a direct catalyst for war.
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Border Disputes: After the annexation of Texas, a dispute arose over the southern boundary of Texas. The U.S. claimed the Rio Grande as the border, while Mexico argued that the boundary was the Nueces River. This disagreement over territory led to skirmishes between Mexican and American troops, further escalating tensions.
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U.S. Expansionist Policies: The United States government, particularly under President James K. Polk, actively sought to expand U.S. territory. Polk's administration was keen on acquiring California and New Mexico and led to open hostilities when American troops entered disputed territories, leading to the Mexican declaration of war after a confrontation in April 1846.
These causes, among others, contributed to the outbreak of the Mexican-American War, which ultimately resulted in significant territorial gains for the United States.