Complex sentence: At the same time as the Spanish expeditions, British mariners also began to explore the region, led by explorers Sir Francis Drake in the 1500s and later by James Cook and George Vancouver in the 1700s.
Split into simpler sentences: At the same time as the Spanish expeditions, British mariners also began to explore the region. Led by explorer's Sir Francis Drake in the 1500s and later by James Cook and George Vancouver in the 1700s.