He signed a loyalty oath to the United States, May 30, 1778 at Valley Forge, Washington, D.C. Shortly afterward, General George Washington made Arnold Commandant of the city of Philadelphia. The war continued and he grew resentful of being passed over for promotion. By 1780 he was in contact with the British Army. Around this time, George Washing gave Arnold command of West Point, a critical American fort on the Hudson River in NY. He reached out to British commander, Sir Henry Clinton, and offered to hand over the fort in exchange for a high military rank and money. On Sept. 21, 1780, Arnold
met with Major Andre at West Point to finalize the deal. as the major was leaving, American officers intervened and discovered papers exposing the plot. Andre was executed and Arnold escaped to NY, behind British lines. After the plot was revealed he was hated by American Patriots so in 1781 he and his family moved to London. He had difficulty finding employment due to his traitorous actions in the U.S. In 1801 he was diagnosed with "dropsy" (edema caused by congestive heart failure) and died on June 14, 1801.