This may be related to the Mexican-American War as they both created the divide between the two countries. During the Mexican-American War, because of America's belief in Manifest Destiny, Americans believed they had the right to conquer their land from coast to coast. This would divide the two countries because Mexico did not want to give up its land, but because of America's desire to move forward, a war broke out. It's similar to the Civil War because people were separated because the North believed slavery should be abolished, while the South believed slavery should be abolished.