Final answer:
The Treaty of Guadalupe Hidalgo concluded the Mexican American War and ceded a large expanse of land to the U.S. known as the Mexican Cession, which is the correct answer to the given question.
Step-by-step explanation:
The Mexican-American War concluded with the Treaty of Guadalupe Hidalgo, which was signed in February 1848. Through this treaty, the Mexican Cession was established, and the United States acquired a vast expanse of land. The land that the U.S. obtained through the treaty eventually became all of, or parts of, the states of California, Arizona New Mexico, Nevada, Utah, Colorado, Wyoming, and Kansas, thereby significantly increasing the nation's territory and bolstering the concept of Manifest Destiny.