The majority of the border follows the Rio Grande River.
He was the first European to discover America, or at least what Europe knew of. Before he discovered it Europe had no knowledge of it existing.America was discovered before by Vikings, by Leif Ericson, but their settlement didn't last that long. Columbus was the first to go to America and maintain contact with the continent and colonize it,having big impact in history. That's why it is better to say - to avoid discussions - that he re-discovered itw
