Complex sentence: Areas noted along the Ramapo River were inhabited by bands of the Lenape tribe, a large group who inhabited much of the coastal areas of the mid-Atlantic region and retreated to the mountains under pressure from Dutch and English colonists.
Split into simpler sentences: Areas noted along the Ramapo River were inhabited by bands of the Lenape tribe, a large group who inhabited much of the coastal areas of the mid-Atlantic region. Some of their people retreated to the mountains under pressure from Dutch and English colonists.