Why Is there Such Contention Over the Texas-Mexican Border? The border between Mexico and the United States has long been a sore spot with repercussions up to the present day. It all started with the Texas Revolution. The end-result: Texas became the 28th state to enter the Union. But it also foreshadowed one of the darkest periods in American history. At the end of the Mexican-American War, Mexico ceded more land to the United States than was acquired in the Louisiana Purchase, which produced other profound effects on the history of both the US and Mexico. There are many important milestones from this war: - Why the slogan, "Remember the Alamo" was so powerful and rallied troops from all over the country to help Texans gain their independence. - How the issue of slavery in the new territories launched the American Civil War thirteen years in the future. - Soldiers fighting as comrades in the Mexican-American War became prominent generals, both North and South, and faced each other as enemies in the Civil war.