Complex sentence: Vincent was in a position to be flanked and his attack had just been repulsed, he quickly decided that Fort George was to be abandoned and withdrew with such haste that women and children were left behind in the fort.
Split into simpler sentences: Vincent was in a position to be flanked, and his attack had just been repulsed. He quickly decided that Fort George should be abandoned and withdrew with such haste that women and children were left behind in the fort.