Question

What events affected the borders in the US? I'll take any.

Answer 1

"Also called the Transcontinental Treaty of 1819, the Adams-Onis Treaty was one of the critical events that defined the U.S.-Mexico border. The border between the then-Spanish lands and American territory was a source of heated international debate. In Europe, Spain was in the midst of serious internal problems and its colonies out west were on the brink of revolution. "

http://www.pbs.org/kpbs/theborder/history/timeline/2.html

"Through the Louisiana Purchase of 1803 and treaties with Spain and Britain, the nation's borders moved west to the Rocky Mountains, north to the 49th parallel, and south to Florida and the Gulf of Mexico. These boundaries remained essentially intact until the 1840s, when the United States acquired massive territories in the Southwest and on the Pacific Coast."

"With the Adams-Onis Treaty of 1819, Spain settled a long dispute with the United States over its southern border. In return for Florida and the Gulf Coast lands east of the Mississippi River, the United States foreswore all claims to Texas in the west. However, soon after the treaty was in place the Mexican War of Independence ended Spanish rule on the continent and forced Spain to relinquish all rights to Texas. "

http://www.smithsonianeducation.org/educators/lesson_plans/borders/essay2.html

Answer 2

I'm not sure if that's exactly what you're looking for, but I hope it helps :p