Complex sentence: It was believed that the lost colonists of Roanoke Island had attempted to travel to this island, because during the late 16th century this island was known as "Croatoan" and was inhabited by a friendly native tribe.
Split into simpler sentences: It was believed that the lost colonists of Roanoke Island had attempted to travel to this island. This is because during the late 16th century this island was known as "Croatoan" and was inhabited by a friendly native tribe.