Final answer:
The Mexican-American War occurred from 1846 to 1848 and concluded with the Treaty of Guadalupe Hidalgo after the annexation of Texas led to a territorial dispute between the U.S. and Mexico.
Step-by-step explanation:
The Mexican-American War was an armed conflict between the United States and Mexico that took place from 1846 to 1848. The primary cause of the war was a territorial dispute after the annexation of Texas. The U.S. claimed the Rio Grande as the border, while Mexico insisted on the Nueces River as the boundary. This conflict was fueled by the U.S. expansionist policy known as Manifest Destiny and the desire for more land suitable for slaveholding.
President James K. Polk, driven by the idea of America's westward expansion, ultimately ordered troops into the disputed area, leading to the outbreak of war. After several key military victories, including the occupation of Mexico City, the war concluded with the signing of the Treaty of Guadalupe Hidalgo, which resulted in Mexico ceding a significant portion of its territory to the U.S. This newly acquired land eventually became part of several southwestern U.S. states.