Final answer:
The significant result of the Mexican-American War was that the United States experienced increased tension over the issue of slavery as the nation had to decide whether the new territories obtained would be free or slave-holding.
Step-by-step explanation:
A significant result of the Mexican-American War of 1846-1848 was that the United States experienced increasing tension over the issue of slavery. Following the war, the United States acquired a vast territory, including present-day California, Nevada, New Mexico, Arizona, Utah, and parts of Colorado and Wyoming. This massive territory acquisition threw the delicate balance between free and slave states into disarray. The Wilmot Proviso, which sought to prohibit slavery in the new territories, ignited fierce debate and illustrated the nation's sectional divisions. Concerns over whether these regions would permit slavery rekindled the issues that had been temporarily settled by the Missouri Compromise, pointing toward the rising tensions that would eventually culminate in the Civil War.
The annexation of Texas, which occurred before the war in 1845, had already raised questions about the expansion of slavery. The new lands obtained from Mexico further exacerbated this debate. The United States had to address the issue of whether the newly incorporated territories would allow slavery, leading to increased sectional conflict.