In the 18th century, America had a big change. It was on April 30, 1803 when the U.S bought the louisiana land to expand America. After this event, president James Polk wanted more land from Mexico to add to Texas and California. After this war was declared between America and Mexico. After this America won the war, but were they really justified to fight in the first place? I don't think America was justified for 3 reasons, America wanted to expand slavery to more areas, America was annexing the Mexican land, and James Polk provoked the war with Mexico.
The first reason that the U.S. wasn't justified to go to war with Mexico was because America was fighting just to expand slavery. Mexico had already
milligalized slavery a while ago for religious reasons. Americans were basically robbing the land as Charles Sumner said in Document D, “...certainly (Mexico) might justly charge us with disgraceful robbery…” Sumner is saying that the U.S. kind of stole/robbed the land from Mexico. This made the war unjustified.
Another reason why America was not justified to go to war with Mexico was because all they wanted to get more land by annexing. The manifest destiny made it sound like it was gods wish to expand but it wasn't.”...the mobilization of the U.S. army was an outright attack… on Mexico.” stated document B. Mexican government predicted that the war was for America to just get more land. They were proved right after the war ended. This is another reason the war was unjustified.
The last reason that the U.S. wasn't justified to go to war with Mexico was because James Polk provoked the war. There was a debate on what the border between the two countries was. Mexico said it was the Nueces river and America said it was the Rio Grande. James Polk sent American troops to the border of Mexico and the Mexicans had no idea what was going on, they suspected it was an attack so they attached back. James Polk used this as an excuse to start war. “In the eyes of the (Mexican) government, the mobilization of the U.S. army was an outright attack on Mexico.” This is another reason why America was not justified to go to war with Mexico.
To conclude, America was not justified to have a war with Mexico. For these 3 reasons; America wanted to expand slavery, they wanted to take more land than just Texas, and President James Polk provoked the Mexicans into starting a war. Americans won the war, but they were not fighting for the right reasons.