Complex sentence: The Italian explorer Amerigo Vespucci, for whom the Americas are named, on a Spanish charter spent four months exploring the Bahamas in 1499--1500, and mapped a portion of the eastern shore of Andros Island.
Split into simpler sentences: The Italian explorer Amerigo Vespucci, for whom the Americas are named, came on a Spanish charter and spent four months exploring the Bahamas in 1499--1500. He mapped a portion of the eastern shore of Andros Island.