Was the United States Justified in Going to War with Mexico?

Was the United States justified in going to war with Mexico?

"Manifest Destiny" was a popular conversation in 1846. James Polk at that time was president, and he did not dislike the idea of "Manifest Destiny". In the early 1800's the united states was starting to expand, due to the addition of the Louisiana Purchase. Was the United States validated to fight with Mexico? The United States was not justified in going to war with Mexico for the following: Polk caused the war to begin, the United States stole Texas from Mexico, and slavery would expand.

The first reason why I think the war with the United States and Mexico was not justified is, because James Polk provoked the war with Mexico. Polk sent a military force, to take position between the Nueces and the Rio Grande, because Polk believed that this was necessary because Mexico would invade Texas. (Doc C) If president Polk had not been a voracious man, Mexico would have never attacked the United States, and shed American blood on American soil.(Doc B) As a result, sixteen American soldiers were killed, because of Polk's instigation.(Hook exercise)

The second reason why I think the war with Mexico was not justified is because the US stole Texas from Mexico. (Doc C) President Polk ordered troops to arrive at the Rio Grande. This was the disputed territory, which angered Mexico, and caused the Mexican government to attack those troops. This, then lead to the battles of Palo Alto and Resaca de la Palma.(Doc C)

The third reason why I think the war with Mexico and the US was not justified is because slavery would spread. After Mexico achieved their independence from Spain, Mexico had made slavery illegal. (Doc D) During this time, citizens of the US, began to move into Texas. These US citizens believed that by moving into Texas, they would achieve the province to expand, and this province would later become part of the United States. Pretty much, America was steeling something that was not theirs.