On June 16, 1775, 3,000 Massachusetts militias occupied the Mount Banks north of Boston City. The next day, the British army sent more than 2,000 men to compete for the high point. The militias, with poor weapons and little ammunition, defeated the British troops three times, showing an astonishing fighting force, and eventually evacuated the highlands due to the use of ammunition, but the British were injured by more than half and suffered heavy losses.

Under the rapid development of the people's anti-British struggle, on May 10, 1775, the Second Continental Congress was convened in Philadelphia, with delegates from all 13 colonies. The Continental Congress declared the North American colonies at war with Britain on May 15. The meeting decided to issue paper money, buy weapons from abroad, recruit volunteers, reorganize the militia gathered in the suburbs of Boston into the "Continental Army", and appoint George Washington as the commander-in-chief of the Continental Army.

After Washington took office, he led the Continental Army to encircle the British army in Boston, cut off the British army's land supply line, and occupied the Doylchester Heights in the south of the city. On March 17, 1776, British troops were forced to withdraw from Boston. According to John. Adams' motion (it was Adams who originally proposed to appoint Washington as commander-in-chief), the Continental Congress unanimously passed a resolution thanking him and ordering the casting of a gold medal bearing the portrait of Washington, the Liberator of Boston, to commemorate the British evacuation of Boston.