The correct option that explains how the Mexican-American War increased the number of Hispanics living in the U.S. is:
• Because of the changed border, many Mexicans became Americans.
This is due to the Treaty of Guadalupe Hidalgo (1848), which ended the war and resulted in Mexico ceding a significant portion of its territory to the United States. As a result, many Mexicans who lived in these newly acquired territories found themselves living within U.S. borders.