Final answer:
Washington used Dorchester Heights to gain a tactical advantage by moving his army stealthily and fortifying the position with cannons, forcing the British to withdraw from Boston.
Step-by-step explanation:
George Washington barricaded his army on Dorchester Heights in March 1776 because it was a strategic move that provided a tactical advantage over the British forces in Boston. Washington's bold plan involved deception, utilizing troops from Pennsylvania to simulate a larger force, while his troops silently moved away in stealth using the dark and rain to their advantage. By the time the British realized Washington and his 9,000 soldiers had left, the Americans had already fortified their position and positioned cannons overlooking both the British fortifications and Boston Harbor, a position from which the British could not effectively return fire.
The British recognized their untenable position, as they could not elevate their cannons to match the American positions on the high ground. This strategic maneuver by Washington forced the British to eventually withdraw their troops to Halifax, Nova Scotia on March 17, 1776, marking the end of the nearly year-long siege of Boston.