The correct response is:
Because of the changed border, many Mexicans became Americans.
The Mexican-American War resulted in the U.S. gaining a significant amount of territory, including present-day California, Arizona, New Mexico, Nevada, Utah, and parts of Colorado and Wyoming. As a result, many Mexicans who lived in these newly acquired territories found themselves living in the United States and were granted U.S. citizenship, thus increasing the number of Hispanics living in the U.S.