Answer:
The Mexican War was justified under the principle of Manifest Destiny.
Explanation:
The Mexican-American War was the first major conflict driven by the ideas of Manifest Destiny, namely the belief that the United States had the God-given right to expand its borders across America, civilizing it. The conflict took place between the United States and Mexico between 1846 and 1848, starting with the annexion of Texas to the United States, and had huge consequences for the future of the nations involved. With the intervention, the United States expanded its territory by about a quarter (25%), while Mexico lost approximately half of its territory (50%).
Among the reasons that led the United States to create the military conflict, the main ones were migratory pressure, the need for new territories and the potential riches of California.