The British force in Boston under Lieutenant General Thomas Gage was sent to Concord, Massachusetts in April of 1775 to confiscate the weapons of the local militia there. When the British regulars and Lexington militia opened fire and the Concord militia mobilized, a running battle was fought all the way back to Boston, where the British army was trapped in-place, and the siege of Boston began.

The "Continental Army" at that time -- mostly just militia from the Boston area, really -- had risen because their property (their weapons) were under threat from being confiscated by the British Army. Of course, the Continental Congress realized that these militiamen were not only pissed at that, but likely at the other acts of Parliament and the King: the Stamp Act, the Boston Massacre, and the much more recent Intolerable Acts, which General Gage had been ordered to uphold. An army fighting for their right to defense of their property was quickly molded into an army fighting for total independence from Great Britain following the Declaration of Independence. The militia eventually laid siege to Boston and forced out the resident British regular army (and Gage himself) after Bunker Hill because they knew that the only way to effectively secure their right to self-defense was to remove the only threat: the local British forces, which themselves held up the word of the King and of Parliament and, thus, the much-hated Intolerable Acts.