Complex sentence: The Norsemen, the Portuguese and the Spanish were the first to explore and to cross it systematically, from Europe to the Americas, as well as by its islands and archipelagos, and from the North Atlantic to the South Atlantic.
Split into simpler sentences: The Norsemen, the Portuguese and the Spanish were the first to explore it. The Spanish were also the first to cross it systematically, from Europe to the Americas, specifically from the North Atlantic to the South Atlantic.