Fighting broke out on 19 April 1775: the British garrison at Boston was harassed by Massachusetts militia at Lexington and Concord after destroying colonial Assembly powder stores. In June the Second Continental Congress appointed George Washington to create a Continental Army and oversee the capture of Boston. The Patriots sent their Olive Branch Petition to the King and Parliament, both of whom rebuffed it. In response they invaded British Quebec but were repulsed. In July 1776, Congress unanimously passed the Declaration of Independence. Hopes of a quick settlement were supported by American sympathizers within Parliament who opposed Lord North's "coercion policy" in the colonies. However, after the British were driven out of Boston the new British commander-in-chief, General Sir William Howe, launched a counter-offensive and captured New York City. After crossing the Delaware Washington engaged and routed Hessian forces at the Battle of Trenton and the British at the Battle of Princeton. After British General Burgoyne surrendered at the Battles of Saratoga in October 1777, Howe's 1777–1778 Philadelphia campaign captured that city. Washington retreated to Valley Forge during the winter of 1777–1778 where Prussian allied General von Steuben drilled the largely untrained Continental Army into an organized fighting unit.