What led to the outbreak of the US-Mexico War?

After the war of independence, the American ruling group has always regarded the expansion to the west as a national policy, especially the slave owners group in the south, and even acted as a deep-water bomb for territorial expansion. The number of immigrants in the western United States has surged, with 1835 reaching 30,000, as far away as California and New Mexico. Migrants often have disputes with the Mexican government. 1835, the U.S. government instigated the Texas slave owners to launch an armed rebellion, and Mexico sent troops to suppress it and annihilated the U.S. troops in the Alamo 187. The United States sent troops to defeat the Mexican army, declared Texas "independent" and established "Xiong Xingguo". 1844 general election, Polk was elected president of the United States, ready to go to war with Mexico. /kloc-0 announced the annexation of Texas in July, 845. At the same time, the United States has stepped up its invasion of other Mexican territories. In order to annex large areas of land in New Mexico and California, on May 1846, the United States declared war on Mexico and the US-Mexico War broke out.