The military career of Benedict Arnold from 1777 to 1779 was marked by two important events in his career. In July 1777, Arnold was assigned to the Continental Army's Northern Department, where he played pivotal roles in bringing about the failure of British Brigadier Barry St. Leger's siege of Fort Stanwix and the American success in the battles of Saratoga, which fundamentally altered the course of the war.
After convalescing following the significant injuries to his leg sustained at Saratoga, Arnold was given military command of Philadelphia after the British withdrawal in 1778. There Arnold became embroiled in political and legal wrangling with enemies in Congress, the army, and the Pennsylvania and Philadelphia governments that undoubtedly contributed to his decision to change sides. In 1779 he began secret negotiations with the British that culminated in a plot to surrender West Point. The plot was exposed in September 1780, following which Arnold fled to British-occupied New York City.
Benedict Arnold was born in 1741 family in the port city of Norwich in the British colony of Connecticut. He was interested in military affairs from an early age, serving briefly (without seeing action) in the colonial militia during the French and Indian War in 1757. He embarked on a career as a businessman, first opening a shop in New Haven, and then engaging in overseas trade. He owned and operated ships, sailing to the West Indies, New France and Europe. When the British Parliament began to impose taxes on its colonies, Arnold's businesses began to be affected by them, and he eventually joined the opposition to those measures. In 1767 he married a local woman, with whom he had three children, one of whom died in infancy. She died in 1775, and Arnold left his children under the care of his sister Hannah at his home in New Haven.
Arnold had distinguished himself early in the war, participating in the capture of Fort Ticonderoga in May 1775 and then boldly leading a raid on Fort Saint-Jean near Montreal. He then led a small army from Cambridge, Massachusetts to Quebec City on an expedition through the wilderness of present-day Maine, where he was wounded in the climactic Battle of Quebec on December 31, 1775. He then presided over an ineffectual siege of Quebec until April 1776, when he took over the military command of Montreal. He directed the American retreat from there on the arrival of British reinforcements, and his forces formed the rear guard of the retreating Continental Army as it headed south toward Ticonderoga. Arnold then organized the defense of Lake Champlain, and led the Continental Navy fleet that was defeated in the October 1776 Battle of Valcour Island.
During these actions, Arnold made a number of friends and a larger number of enemies within the army power structure and in Congress. He had established decent relationships with George Washington, commander of the army, as well as Philip Schuyler and Horatio Gates, both of whom had command of the army's Northern Department during 1775 and 1776. However, an acrimonious dispute with Moses Hazen, commander of the 2nd Canadian Regiment, boiled over into a court martial of Hazen at Ticonderoga during the summer of 1776. Only action by Gates, then his superior at Ticonderoga, prevented his own arrest on countercharges levelled by Hazen. He had also had disagreements with John Brown and James Easton, two lower-level officers with political connections that resulted in ongoing suggestions of improprieties on his part. Brown was particularly vicious, publishing a handbill that claimed of Arnold, "Money is this man's God, and to get enough of it he would sacrifice his country".