The question of whether the United States was justified in going to war with Mexico in the 1840s is a complex and highly debated issue. One of the main reasons for the conflict was the annexation of Texas by the United States in 1845, which Mexico saw as a violation of its sovereignty. Mexico also claimed that the border between Texas and Mexico was the Nueces River, while the United States claimed it was the Rio Grande. The disagreement over the border led to military skirmishes and eventually, in 1846, the United States declared war on Mexico.
One argument for the justification of the war is the idea of manifest destiny. Which held that the United States was destined to expand its territory and spread its ideals of freedom and democracy. Proponents of manifest destiny saw the annexation of Texas and the conquest of Mexico as necessary steps towards fulfilling this destiny. They also claimed that Mexico was a backwards and uncivilized nation that would benefit from being brought under the control of the United States.
On the other hand, there are many who argue that the United States was not justified in going to war with Mexico. They point out that the annexation of Texas was a violation of Mexican sovereignty and that the United States had no right to take over another country's territory. They also argue that the idea of manifest destiny was a guise for imperialism and territorial expansion. And that the United States was not truly motivated by a desire to spread democracy and freedom.
Another criticism of the war is the treatment of Mexican citizens by the United States during and after the conflict. The Treaty of Guadalupe Hidalgo, which ended the war, forced Mexico to cede a large portion of its territory to the United States. That includes modern-day California, Nevada, Utah, Arizona, New Mexico, Texas, and parts of Colorado, Wyoming, Kansas, and Oklahoma. This resulted in the displacement of many Mexican citizens and a long-standing cultural and political conflict between the two countries.
In conclusion, the question of whether the United States was justified in going to war with Mexico is a highly complex and controversial issue. Proponents of the war point to manifest destiny and the idea of spreading democracy and freedom, while critics argue that it was a violation of Mexican sovereignty and an act of imperialism. Regardless of one's stance on the issue, the war had lasting and significant impacts on both the United States and Mexico. And it continues to be a topic of debate and discussion.