Benedict Arnold's treason exposed

In September 1780, Benedict Arnold's plot to surrender West Point to the British was exposed after Major John Andre was captured near Tarrytown, New York, on September 23. Arnold had secretly negotiated with General Henry Clinton while commanding the American fortifications at West Point on the Hudson River. When Andre's papers revealed the scheme, Arnold escaped to British lines and entered British service.

Arnold's betrayal intensified a dangerous military and political tension because West Point guarded the Hudson corridor linking New England to the rest of the United States. If Clinton had gained West Point in 1780, the British might have split the American states strategically even after the French alliance had changed the war. The exposure of the plot also shocked the Continental Army by showing that personal grievance and debt could corrupt even one of its most celebrated battlefield officers.

Andre's capture led to his execution as a spy on October 2, 1780, while Arnold spent the rest of the war leading British raids in Virginia and Connecticut. The failed treason preserved West Point for Washington and prevented a British success that might have altered the northern war in 1780.