Complex sentence: The Harmonites were Christian pietist separatists who split from the Lutheran Church in the late 18th century, and under the leadership of George Rapp left Württemberg, Germany, and came to the United States in 1803.
Split into simpler sentences: The Harmonites were Christian pietist Separatists who split from the Lutheran Church in the late 18th century. Under the leadership of George Rapp, the group left Württemberg, Germany, and came to the United States in 1803.