Complex sentence: Clark and his men captured Kaskaskia (currently Illinois) on July 4,1778 and Cahokia July 6,1778, during the battle of Kaskaskia, Clark split his force, commanding one half himself with Captain Helm commanding the other.
Split into simpler sentences: Clark and his men captured Kaskaskia, Illinois on July 4,1778 and Cahokia, Illinois July 6,1778. During the capture of Kaskaskia, Clark split his force, commanding one half himself with Captain Helm commanding the other.