Final answer:
Manifest Destiny justified the United States' expansion goals, which led to the Mexican American War and the acquisition of new territories.
Step-by-step explanation:
The term 'Manifest Destiny' relates to the Mexican American War because it was the ideology that justified the expansionist goals of the United States during that time. Manifest Destiny was the belief that the United States was destined to spread its democratic institutions and control over the entire continent of North America, from the Atlantic to the Pacific Ocean.
This belief led to the acquisition of new territories, including Texas, Oregon, and California, which ultimately resulted in the war with Mexico in the 1840s. The Mexican American War was a direct result of the United States' desire to expand its territory. The annexation of Texas in 1845 sparked tensions between the United States and Mexico, as Mexico still considered Texas as its own territory.
The war erupted in 1846 and lasted for two years, ending with the Treaty of Guadalupe Hidalgo in 1848. Through this treaty, Mexico was forced to cede a vast amount of territory to the United States, including present-day California, Nevada, Utah, Arizona, New Mexico, and parts of Colorado, Wyoming, Kansas, and Oklahoma.
Therefore, it can be said that the concept of Manifest Destiny was the underlying idea behind the United States' motives for expansion and ultimately led to the Mexican American War, which resulted in significant territorial gains for the United States.