Complex sentence: The Anabaptist religions promoted a simple lifestyle and their adherents were known as Plain people or Plain Dutch, as opposed to the Fancy Dutch who tended to assimilate more easily into the American mainstream.
Split into simpler sentences: The Anabaptist religions promoted a simple lifestyle and their adherents were known as Plain people or Plain Dutch. This was in contrast to the Fancy Dutch, who tended to assimilate more easily into the American mainstream.