John L. O'Sullivan

Doctrine of Discovery: A principle of international law dating from the late 15th century granting rights over indigenous lands discovered by European explorers – think about finding a hidden treasure first and claiming ownership over it.

Mexican-American War (1846-1848): A war between the U.S and Mexico following the U.S annexation of Texas, which Mexico still considered its territory. It's like a fight breaking out after someone takes another person's seat, even though that person was not currently sitting there.

Treaty of Guadalupe Hidalgo: The treaty that ended the Mexican-American War in 1848, leading to significant territorial gains for the United States. Imagine settling an argument with your sibling by getting most of their candy stash.