Final answer:
Washington gained control of Boston through the strategic placement of cannons on Dorchester Heights, which forced British evacuation in March 1776. The success at Dorchester was part of a larger conflict where the Continental Army gradually became more capable under Washington's leadership, contributing to key victories such as the Battle of Saratoga.
Step-by-step explanation:
The pivotal moment where General George Washington gained control of Boston came with the strategic use of artillery from Fort Ticonderoga. Under Washington's command, the Continental Army fortified Dorchester Heights with these cannons, which had been transported overland in a remarkable feat of logistics. Overlooking the city and the harbor, this positioning threatened the British fleet and forced General Howe to make a choice: assault the heights and suffer potentially severe casualties or evacuate. Howe chose to evacuate, and on March 17, 1776, the British and their Loyalist supporters sailed away from Boston, handing Washington and the Continental Army a significant victory. This event is commemorated as Evacuation Day in Massachusetts.
British strategy had been to subdue the unrest in New England, especially after the instigation of the Massachusetts Circular and the deployment of additional troops in response to the growing rebellion. Yet, despite attempts to assert control, including the enforcement of the Coercive Acts and Gage's command in Boston, tensions rose to breaking points such as the battles at Lexington, Concord, and ultimately, the siege that led to the British evacuation of Boston.
The successful American stand at The Battle of Harlem Heights later in 1776, which occurred after the British takeover of New York City, and the significant defeat of British forces in the Battle of Saratoga in 1777 illustrated the Continental Army's growing capabilities under Washington's leadership.