Complex sentence: One such example was the opposing irregular forces operating in Missouri and northern Arkansas from 1862 to 1865, most of which were pro-Confederate or pro-Union in name only and preyed on civilians and isolated military forces of both sides with little regard of politics.
Split into simpler sentences: One such example was the opposing irregular forces operating in Missouri and northern Arkansas from 1862 to 1865, most of which were pro-Confederate or pro-Union in name only. They preyed on civilians and isolated military forces of both sides with little regard of politics.