According to the U.S. Army, military leader and future President Ulysses S. Grant called the war “one of the most unjust ever waged by a stronger against a weaker nation.” He and others who opposed the war, like Transcendentalist writer Henry David Thoreau, knew that the Mexican-American War happened because of the country’s rabid lust for expansion of territory and power known as Manifest Destiny. However, not everyone had the same negative opinion of the war. As they are wont to do, Americans were divided in their support or disapprobation of the conflict, and once it was finally over, they had even more to argue about.

Now there was the question of slavery. Would the country expand the disgraceful institution to the newly acquired territories or would they be free? And as the American Battlefield Trust notes, the debate over what to do dissolved party lines, rang the death knell for the Whig Party, and led to the creation of the Republican Party, which began as a party opposed to exploitative practices like slavery. But the political tensions were not settled by the formation of the new party. They continued to seethe until the country exploded into all-out civil war, and the American people are still divided over that conflict to this day. There are those who believe in the Lost Cause of the Confederacy— a pseudo-history propagating a false narrative of southern victory in the Civil War and good intentions for hateful practices like slavery — and then there are those who believe the truth.