Complex sentence: The Appalachian region was largely settled in the 18th century by the Ulster Scots, Protestants who migrated to the Irish province of Ulster during the Plantation of Ulster in the 17th century.
Split into simpler sentences: The Appalachian region was largely settled in the 18th century by the Ulster Scots. The Ulster Scots were Protestants who migrated to the Irish province of Ulster during the Plantation of Ulster in the 17th century.