Who was the American president during the wartime treaty of 1848 that altered national boundaries greatly?

The American president during the wartime treaty of 1848 that significantly altered national boundaries was James Polk. This treaty, known as the Treaty of Guadalupe Hidalgo, concluded the Mexican-American War and resulted in the United States acquiring a vast amount of territory, including present-day California, Arizona, New Mexico, Nevada, Utah, and parts of Colorado and Wyoming.

Polk was a strong proponent of westward expansion, a belief often referred to as Manifest Destiny, which aimed to extend the United States across the North American continent. His administration's focus on this expansionist policy played a crucial role in negotiating the treaty and incorporating this newly acquired land into the United States, thereby reshaping the nation’s borders and influencing its future development.