The Mexican-American War was a conflict that took place between 1846 and 1848 between the United States and Mexico. It stemmed from disputes over the annexation of the Republic of Texas, which had declared independence from Mexico in 1836 but was eventually admitted as a state into the United States in 1845. Mexico never recognized Texas' independence or its annexation by the United States.
The war began when the U.S. President James Polk ordered troops to the disputed area between the Nueces and Rio Grande rivers, which both countries claimed as their border. The U.S. forces clashed with Mexican troops, and the conflict escalated into a full-fledged war. The U.S. forces, better equipped and with superior military strategy, won significant victories throughout the conflict, leading to the capture of Mexico City and ultimately the Treaty of Guadalupe Hidalgo, which ended the war.
The question of whether the Mexican-American War was justified is a matter of historical interpretation and political perspective. Supporters of the war argued that it was necessary for the expansion of the United States and the fulfillment of its manifest destiny, the belief that the U.S. had the right and obligation to expand its territory from coast to coast. They saw the conflict as a justifiable response to Mexican aggression against U.S. territory and interests.
Opponents of the war, however, criticized it as an unjust act of aggression and imperialism by the United States. They argued that the U.S. provoked the conflict by annexing Texas and claimed that the U.S. was primarily motivated by the desire to expand slavery into new territories, as Texas was a slave state. Opponents also pointed out that Mexico was a weaker and less developed nation that was essentially invaded by a much stronger power.
It is important to note that the war also had significant implications for Mexico, resulting in the loss of almost half of its territory, including present-day California, Nevada, Utah, Arizona, New Mexico, Texas, and parts of Colorado, Wyoming, Kansas, and Oklahoma.
Overall, opinions on the justification of the Mexican-American War vary, and different interpretations consider factors such as political, economic, cultural, and territorial motives.