(Definition of harp on (about sth) from the Cambridge Advanced Learners Dictionary & Thesaurus Â© Cambridge University Press).
Battle of Saratoga. In late September and during the first week of October 1777, Gate's American army was positioned between Burgoyne's army and Albany. On October 7, Burgoyne took the offensive. The troops crashed together south of the town of Saratoga, and Burgoyne's army was broken. In mop-up operations 86 percent of Burgoyne's command was captured.
The Battle of Saratoga was probably the most important point in the war. British General John Burgoyne led a large invasion army southward from Canada in the Champlain Valley, hoping to meet a similar British force marching northward from New York City and another British force marching eastward from Lake Ontario.