Complex sentence: His first military engagement against the British was on September 11 1777, at the Battle of Brandywine, and his courageous charge in this engagement averted a disastrous defeat of the American cavalry and saved the life of George Washington.
Split into simpler sentences: His first military engagement against the British was on September 11 1777, at the Battle of Brandywine. His courageous charge averted a disastrous defeat of the American cavalry and saved the life of George Washington.