Boston campaign The Boston campaign was the opening campaign of the American Revolutionary War . The campaign was primarily concerned with the mobilization of Patriot militia units , and their transformation into a unified Continental Army . The campaign ' s military conflicts started with the Battles of Lexington and Concord on April 19 , 1775 , in which militias turned out according to plan to interdict and harass the British attempt to seize military stores and leaders in Concord , Massachusetts . The entire British expedition suffered significant casualties during a running battle back to Charlestown against an ever - growing number of militia . The accumulated militia surrounded the city of Boston , beginning the Siege of Boston . The main action during the siege , the Battle of Bunker Hill on June 17 , 1775 , was one of the bloodiest encounters of the entire war . There were also numerous skirmishes near Boston and the coastal areas of Boston , resulting in either loss of life , military supplies , or both . In July 1775 , George Washington took command of the assembled militia and transformed them into a more coherent army . On March 4 , 1776 , the Patriot army fortified Dorchester Heights with cannon capable of reaching Boston and British ships in the harbor . The siege ( and the campaign ) ended on March 17 , 1776 , with the withdrawal of British forces from Boston . Background . In 1767 , the British Parliament passed the Townshend Acts , which imposed import duties on paper , glass , paint , and other common items imported into the American colonies . The Sons of Liberty and other Patriot organizations responded with a variety of protest actions . They organized boycotts of the goods subject to the duty , and they harassed and threatened the customs personnel who collected the duties , many of whom were either corrupt or related to Provincial leaders . Francis Bernard , then Governor of the Province of Massachusetts Bay , requested military forces to protect the King ' s personnel . In October 1768 , British troops arrived in the city of Boston and occupied the city . Tensions led to the Boston Massacre on March 5 , 1770 , and the Boston Tea Party on December 16 , 1773 . In response to the Tea Party and other protests , Parliament enacted the Intolerable Acts to punish the colonies . With the Massachusetts Government Act of 1774 it effectively abolished the provincial government of Massachusetts . General Thomas Gage , already the commander - in - chief of British troops in North America , was also appointed governor of Massachusetts and was instructed by King George ' s government to enforce royal authority in the troublesome colony . However , popular resistance compelled the newly appointed royal officials in Massachusetts to resign or to seek refuge in Boston . Gage commanded four regiment s of British regulars ( about 4 , 000 men ) from his headquarters in Boston , but the countryside was largely controlled by Patriot sympathizers . War begins . On September 1 , 1774 , British soldiers removed gunpowder and other military supplies in a surprise raid on a powder magazine near Boston . This expedition alarmed the countryside , and thousands of American Patriots sprang into action , amid rumors that war was at hand . Although it proved to be a false alarm , this event — known as the Powder Alarm — caused all concerned to proceed more carefully in the days ahead , and essentially provided a " dress rehearsal " for events seven months later . Partly in response to this action , the colonists carried off military supplies from several forts in New England and distributed them among the local militias . On the night of April 18 , 1775 , General Gage sent 700 men to seize munition s stored by the colonial militia at Concord . Several riders — including Paul Revere — alerted the countryside , and when the British troops entered Lexington on the morning of April 19 , they found 77 minutemen formed up on the village common . Shots were exchanged , eight Minutemen were killed , the outnumbered colonial militia dispersed , and the British moved on to Concord . At Concord , the troops searched for military supplies , but found relatively little , as the colonists , having received warnings that such an expedition might happen , had taken steps to hide many of the supplies . During the search , there was a confrontation at the North Bridge . A small company of British troops fired on a much larger column of colonial militia , which returned fire , and eventually rout ed those troops , which returned to the village center and rejoined the other troops there . By the time the " redcoats " or " lobster backs " ( as the British soldiers were called ) began the return march to Boston , several thousand militiamen had gathered along the road . A running fight ensued , and the British detachment suffered heavily before reaching Charlestown . With the Battle of Lexington and Concord — the " shot heard ' round the world " — the war had begun . Siege of Boston . In the aftermath of the failed Concord expedition , the thousands of militiamen that had converged on Boston remained . Over the next few days , more arrived from further afield , including companies from New Hampshire , Connecticut , and Rhode Island . Under the command of Artemas Ward , they surrounded the city , blocking its land approaches and putting the occupied city under siege . The British regulars fortified the high points in the city . Need for supplies . While the British were able to resupply the city by sea , supplies in Boston were short . Troops were sent out to some of the islands in Boston Harbor to raid farmers for supplies . In response , the colonials began clearing those islands of supplies useful to the British . One of these actions was contested by the British in the Battle of Chelsea Creek , but it resulted in the loss of two British soldiers and the British ship " Diana " . The need for building materials and other supplies led Admiral Samuel Graves to authorize a Loyalist merchant to send his ships from Boston to Machias in the District of Maine , accompanied by a Royal Navy schooner . The Machias townspeople rose up , seizing the merchant vessels and then the schooner after a short battle in which its commander was killed . Their resistance and that of other coastal communities led Graves to authorize an expedition of reprisal in October whose sole significant act was the Burning of Falmouth . The outrage in the colonies over this action contributed to the passing of legislation by the Second Continental Congress that established the Continental Navy . The colonial army also had issues with supply , and with command . Its diverse militias needed to be organized , fed , clothed , and armed , and command needed to be coordinated , as each militia leader was responsible to his province ' s congress . Bunker Hill . Late in May , General Gage received by sea about 2 , 000 reinforcements and a trio of generals who would play a vital role in the war : William Howe , John Burgoyne , and Henry Clinton . They formulated a plan to break out of the city , which was finalized on June 12 . Reports of these plans made their way to the commanders of the besieging forces , who decided that additional defensive steps were necessary . On the night of June 16 – 17 , 1775 , a detachment of the colonial army stealthily marched onto the Charlestown peninsula , which the British had abandoned in April , and fortified Bunker Hill and Breed ' s Hill . On June 17 , British forces under General Howe attacked and seized the Charlestown peninsula in the Battle of Bunker Hill . This battle was technically a British victory , but losses ( about 1 / 3 the attacking forces killed or wounded , including a significant fraction of the entire British officer corps in all of North America ) were so heavy that the attack was not followed up . The siege was not broken , and General Gage was recalled to England in September and replaced by General Howe as the British commander - in - chief . Formation of the Continental Army . The Second Continental Congress , meeting in Philadelphia , had received reports of the situation outside Boston when it began to meet in May 1775 . In response to the confusion over command in the camps there , and in response to the May 10 capture of Fort Ticonderoga , the need for unified military organization became clear . Congress officially adopted the forces outside Boston as the Continental Army on May 26 , and named George Washington its commander - in - chief on June 15 . Washington left Philadelphia for Boston on June 21 , but did not learn of the action at Bunker Hill until he reached New York City . Stalemate . Following the Battle of Bunker Hill , the siege was effectively stalemated , as neither side had either a clearly dominant position , or the will and materiel to significantly alter its position . When Washington took command of the army in July , he determined that its size had reduced from 20 , 000 to about 13 , 000 men fit for duty . He also established that the battle had severely depleted the army ' s powder stock , which was eventually alleviated by powder shipments from Philadelphia . The British were also busy bringing in reinforcements ; by the time of Washington ' s arrival the British had more than 10 , 000 men in the city . Throughout the summer and fall of 1775 , both sides dug in , with occasional skirmishes , but neither side chose to take any significant action . Congress , seeking to take some initiative and to capitalize on the capture of Ticonderoga , authorized an invasion of Canada , after several letters to the inhabitants of Canada were rejected by the French - speaking and British colonists there . In September , Benedict Arnold led 1 , 100 troops on an expedition through the wilderness of Maine , which was drawn from the army assembled outside Boston . Washington faced a personnel crisis toward the end of 1775 , as most of the troops in the army had enlistments that expired at the end of 1775 . He introduced a number of recruitment incentives and was able to keep the army sufficiently large to maintain the siege , although it was by then smaller than the besieged forces . Siege ends . By early March 1776 , heavy cannons that had been captured at Fort Ticonderoga were moved to Boston , a difficult feat engineered by Henry Knox . When the guns were placed on Dorchester Heights in the course of one day , overlooking the British positions , the British situation became untenable . While General Howe planned an attack to reclaim the high ground , a snowstorm prevented its execution . The British , after threatening to burn the city if their departure was hindered , evacuated the city on March 17 , 1776 and sailed for temporary refuge in Halifax , Nova Scotia . The local militias dispersed and , in April , General Washington took most of the Continental Army to fortify New York City and the start of the New York and New Jersey campaign . Legacy . The British were essentially driven from New England as a result of this campaign , although there ( as elsewhere in the colonies ) they continued to receive support from local Loyalist s , especially in Newport , Rhode Island , from which they drove most of the local Patriot s . The campaign , as well as the final result of the war as a whole , were a significant blow to British prestige and confidence in its military . The senior military leaders of the campaign were criticized for their actions ( Clinton , for example , while he went on to command the British forces in North America , would take much of the blame for the British loss of the war ) , and others either saw no more action in the war ( Gage ) , or were ultimately disgraced ( Burgoyne , who surrendered his army at Saratoga ) . While the British continued to control the seas , and had military successes on the ground ( notably in New York , New Jersey , and Pennsylvania ) , their actions that led to these conflicts had the effect of uniting the Thirteen Colonies in opposition to the crown . As a result , they were never able to marshal enough support from Loyalists to regain meaningful political control of the colonies . The colonies , in spite of their differences , united themselves as a consequence of these events , granting the Second Continental Congress ( predecessor to the modern U . S . Congress ) sufficient authority and funding to conduct the revolution as a unified whole , including funding and outfitting the military forces that formed as a result of this campaign .