Complex sentence: The organization reached its highest point of power during the years that followed, and by 1925 over half the members of the Indiana General Assembly, the Governor of Indiana, and many other high ranking members of the government were all members of the Klan.
Split into simpler sentences: The organization reached its highest point of power during the years that followed. By 1925 over half the members of the Indiana General Assembly, the Governor of Indiana, and many other high-ranking members of the government belonged to the Klan.