Benedict Arnold was an embittered man, disdainful of his fellow officers and resentful toward Congress for not promoting him more quickly and to even higher rank. A widower, he threw himself into the social life of the city, holding grand parties, courting and marrying Margaret Shippen, "a talented young woman of good family, who at 19, was half his age" and failing deeply into debt. Arnold's extravagance drew him into shady financial schemes and into disrepute with Congress, which investigated his accounts and recommended a court-martial. "Having ... become a cripple in the service of my country, I little expected to meet [such] ungrateful returns," he complained to Washington.
Faced with financial ruin, uncertain of future promotion, and disgusted with congressional politics, Arnold made a fateful decision: he would seek fortune and fame in the service of Great Britain. With cool calculation, he initiated correspondence with Sir Henry Clinton, the British commander, promising to deliver West Point and its 3,000 defenders for 2O,OOO sterling (about $1 million today), a momentous act that he hoped would spark the collapse of the American cause. Persuading Washington to place the fort under his command, Arnold moved in September 1780 to execute his audacious plan. On September 21, British Major Andre came ashore in full uniform near Havestraw from the HM Vulture. There, he met Arnold to finalize the agreement. Unfortunately for them, the Vulture then came under American fire and headed away, leaving Andre stranded. Andre reluctantly donned civilian clothes and headed down the Hudson with a safe conduct pass from Arnold. Near Tarrytown, Andre was captured by three militiamen, who turned him over to the commander at North Castle. Andre was found carrying incriminating papers. When Arnold was notified at breakfast on April 23 that a British officer had been captured, he fled by boat to the Vulture. Andre was later hung as a spy. Arnold received 6,000 Sterling from the British government and an appointment as a brigadier general.
Arnold served George III with the same skill and daring he had shown in the Patriot cause. In 1781 he led devastating strikes on Patriot supply depots: In Virginia he looted Richmond and destroyed munitions and grain intended for the American army opposing Lord Cornwallis; in Connecticut he burned ships, warehouses, and much of the town of New London, a major port for Patriot privateers.
In the end, Benedict Arnold's "moral failure lay not in his disenchantment with the American cause" for many other officers returned to civilian life disgusted with the decline in republican virtue and angry over their failure to win a guaranteed pension from Congress. Nor did his infamy stem from his transfer of allegiance to the British side, for other Patriots chose to become Loyalists, sometimes out of principle but just as often for personal gain. Arnold's perfidy lay in the abuse of his position of authority and trust: he would betray West Point and its garrison "and if necessary the entire American war effort" to secure his own success. His treason was not that of a principled man but that of a selfish one, and he never lived that down. Hated in America as a consort of "Beelzebub ... the Devil," Arnold was treated with coldness and even contempt in Britain. He died as he lived, a man without a country.