linguistic:paraphrasing
Military hostilities begin

King George declared Massachusetts to be in a state of rebellion in February 1775 and the British garrison received orders to seize the rebels' weapons and arrest their leaders, leading to the Battles of Lexington and Concord on April 19, 1775. The Patriots assembled a militia 15,000 strong and laid siege to Boston, occupied by 6500 British soldiers. The Second Continental Congress convened in Philadelphia on June 14, 1775. The congress was divided on the best course of action. They authorized formation of the Continental Army and appointed George Washington as its commander-in-chief, and produced the Olive Branch Petition in which they attempted to come to an accord with King George. The king, however, issued a Proclamation of Rebellion which declared that the states were "in rebellion" and the members of Congress were traitors. The Battle of Bunker Hill followed on June 17, 1775. It was a British victory—but at a great cost: about 1,000 British casualties from a garrison of about 6,000, as compared to 500 American casualties from a much larger force.

As Benjamin Franklin wrote to Joseph Priestley in October 1775:

Britain, at the expense of three millions, has killed 150 Yankees this campaign, which is £20,000 a head... During the same time, 60,000 children have been born in America. From these data his mathematical head will easily calculate the time and expense necessary to kill us all.

In the winter of 1775, the Americans invaded northeastern Quebec under generals Benedict Arnold and Richard Montgomery, expecting to rally sympathetic colonists there. The attack was a failure; many Americans were killed, captured, or died of smallpox.

In March 1776, aided by the fortification of Dorchester Heights with cannons recently captured at Fort Ticonderoga, the Continental Army led by George Washington forced the British to evacuate Boston. The revolutionaries now fully controlled all thirteen colonies and were ready to declare independence. There still were many Loyalists, but they were no longer in control anywhere by July 1776, and all of the Royal officials had fled.