How did the southwestern United States steal it from Mexico?

A large part of the southwestern United States, including California, Texas, New Mexico and other places, was taken away from Mexico by the United States in the19th century American-Mexico War, which was obviously a war of aggression by the United States against Mexico. 1In the 1930s, after decades of domestic stability, the United States gradually developed the ambition of outward expansion. At the same time, the political situation in Mexico was unstable only in the1820s, and the planters in the southern United States hoped to expand more farming areas, and gradually became interested in Texas, which was then Mexico, and began to buy land in Texas at low prices, prompting a large number of Americans to move to Texas. By 1835, there are 30,000 Americans in Texas, more than the population of Mexico. These Americans who moved to Texas organized their own militia and administrative organs, disobeyed Mexican rule, and later provoked Mexican troops. 1836, under the planning of retired American general Houston, the Americans launched a rebellion in Texas, seized the political power in Texas, and announced that Texas was separated from Mexico and established the "Lone Star * * * Republic". Mexico * * * initially refused to recognize Texas and sent troops to crusade. As a result, it was defeated by the Texas army. Mexico recognized Texas at 1837. By 1845, the United States annexed Texas, and Texas became the 28th state in the United States. Mexico is very dissatisfied with the United States from infiltrating Texas to inciting Texas and then annexing Texas. Because the border issue with the United States is still unresolved, it is decided to break diplomatic relations with the United States, and the relationship between the United States and Mexico is tense. At that time, the United States was not satisfied with the annexation of Texas, hoping to get more benefits from Mexico, so it took the opportunity to use force against Mexico, which triggered the US-Mexico War. During 1845, the United States sent more troops to Texas. Later, on May 1846, the United States declared war on Mexico and sent troops across the border to invade Mexico. At that time, the territory of northern Mexico, including California and New Mexico, was attacked by the US military. Among them, American immigrants from California imitated American immigrants from Texas and launched a rebellion. With the help of American troops, they attacked the Mexican Ministry in California. Finally,1In June, 846, California announced its separation from Mexico and merged into the United States two months later. On the other hand, American troops occupied New Mexico and incorporated it into the United States. American troops continue to move south. By the end of 1846, the United States had occupied one third of Mexico's territory. However, Mexico still refuses to give in to the United States. The war continued until 1847. At one time, Mexico made a slight counterattack against Saarti, a major northern town captured by the United States. Both sides suffered heavy casualties, but Mexico's counterattack was repelled by the United States. However, due to Mexico's stubborn resistance on the land front, the US military landed in central Mexico from the sea in an attempt to attack Mexico City. However, the American army was still fiercely resisted by Mexicans, and it took half a year to capture Mexico City. At this time, the old Mexico was overthrown by the people. 1848 In February, the United States and Mexico signed a peace treaty in Guadalupe Hidalgo, a small town north of Mexico City. Mexico agreed to cede northern territories such as California, New Mexico, Nevada, Utah, Arizona and Wyoming to the United States, and the United States gave Mexico15 million dollars as compensation, and forgave Mexico's debts owed to the United States. The US-Mexico War was the first war of American expansion. After this war, the United States and Mexico relocated in North America, and the United States seized rich places such as Texas, California and New Mexico, expanded to the west of the North American continent and the east coast of the Pacific Ocean, and took an important step towards the ranks of world powers. On the contrary, Mexico lost one-third of its territory in the war and was unable to compete with the United States.

Reference: Zhang Jiazhe: Latin America: From Indian Civilization to Modernization