Identify various examples of how the United States changed during this time period. Manifest destiny

What time period are you referring to?

With its triumph in the Mexican-American War, the United States seemingly realized its Manifest Destiny by gaining an immense domain (more than 525,000 square miles [1,360,000 square km] of land), including present-day Arizona, California, western Colorado, Nevada, New Mexico, Texas, and Utah.

Manifest Destiny, in U.S. history, the supposed inevitability of the continued territorial expansion of the boundaries of the United States westward to the Pacific and beyond. Before the American Civil War (1861–65), the idea of Manifest Destiny was used to validate continental acquisitions in the Oregon Country, Texas, New Mexico, and California. The purchase of Alaska after the Civil War briefly revived the concept of Manifest Destiny, but it most evidently became a renewed force in U.S. foreign policy in the 1890s, when the country went to war with Spain, annexed Hawaii, and laid plans for an isthmian canal across Central America.

Explanation:

https://www.britannica.com/event/Manifest-Destiny

d) a constitutional amendment