By 1770, the financially strapped British government had abandoned Fort Ontario and most other Great Lakes frontier army posts while shifting regular troops mainly to seacoast towns, and after Parliament passed the Quartering Act of 1765 and then, following the Boston Tea Party, the Coersive Acts of 1774, including another Quartering Act that let Royal Governors quarter soldiers in unoccupied buildings, rising tensions helped spark the opening hostilities of the Revolutionary War at Lexington and Concord, Massachusetts, on April 19, 1775. Shortly after the war began, Fort Ontario became a temporary shelter for Loyalist refugees driven from the Mohawk Valley, and their wartime exodus through the fort led to new settlements along the north shore of Lake Ontario and the Niagara frontier. In June 1775, British Indian Superintendent Colonel Guy Johnson held a conference there with more than 1300 Haudenosaunee leaders, seeking support against the rebels, but they did not unite behind him; some Mohawks led by Joseph Brant followed Johnson to Canada after the conference ended on July 8, 1775, while the Haudenosaunee remained divided between Crown and rebel adherents and found neutrality difficult. In 1777, a British campaign aimed to use New York’s waterways for victory, with Brigadier General Barry St. Leger moving from Fort Ontario along the Oswego-Oneida-Mohawk river route toward Albany to join other British forces, but after stiff resistance at Fort Schuyler, the battle near Oriskany on August 6, and an unsuccessful bombardment, he abandoned the siege on August 26, returned to Fort Ontario, and then withdrew to Canada with the fort’s garrison and artillery; Continental troops from Fort Schuyler occupied the fort’s abandoned buildings in July 1778. Under pressure from the Haudenosaunee, Governor-general of Canada Major General Frederick Haldimand ordered Major John Ross to rebuild and garrison Fort Ontario in April 1782, and fearing another invasion of the Mohawk Valley, Lieutenant General George Washington ordered Colonel Marinus Willet to make a surprise winter attack, but when Willet’s Oneida guide became lost and his force appeared in view of the fort at sunrise on February 12th, 1783, the attack failed and his frozen troops returned, ending the last Continental Army campaign of the Revolutionary War. Although the Treaty of Paris on September 3, 1783, ended the war and Great Britain recognized the United States, Britain held Fort Ontario and six other Northwest Posts until 1796, using them as leverage over compensation for seized Loyalist property, blocking American settlement near the mouth of the Oswego River, and imposing duties on American salt cargoes from Salina, until United States troops under Captain James Bruff replaced the last British garrison on July 14, 1796, and the American flag was raised over the fort for the first time.