Invasion of Canada (1775) in the context of Siege of Fort St. Jean

The Green Mountain Boys were a militia organization established in 1770 in the territory between the British provinces of New York and New Hampshire, known as the New Hampshire Grants and later in 1777 as the Vermont Republic (which later became the state of Vermont). Headed by Ethan Allen and members of his extended family, it was instrumental in resisting New York's attempts to control the territory, over which it had won de jure control in a territorial dispute with New Hampshire.

Some companies served in the American Revolutionary War, including notably when the Green Mountain Boys, led under the command of Ethan Allen while being assisted by Benedict Arnold, captured Fort Ticonderoga on Lake Champlain on May 10, 1775, and invaded Canada later in 1775. In early June 1775, Ethan Allen and his then subordinate, Seth Warner, induced the Continental Congress at Philadelphia to create a Continental Army ranger regiment from the then New Hampshire Grants. Having no treasury, the Congress directed that New York's revolutionary Congress pay for the newly authorized regiment. In July 1775, Allen's militia was granted support from the New York revolutionary Congress.

General Guy Carleton, 1st Baron Dorchester, KB (3 September 1724 – 10 November 1808), known between 1776 and 1786 as Sir Guy Carleton, was a British Army officer and colonial administrator. He twice served as Governor of the Province of Quebec, from 1768 to 1778, concurrently serving as Governor General of British North America in that time, and again from 1785 to 1795. The title Baron Dorchester was created on 21 August 1786.

He commanded British troops in the American Revolutionary War, first leading the defence of Quebec during the 1775 rebel invasion, and the 1776 counteroffensive that drove the rebels from the province. In 1782 and 1783, he led as the commander-in-chief of all British forces in North America. In this capacity he was notable for carrying out the Crown's promise of freedom to slaves who joined the British, and he oversaw the evacuation of British forces, Loyalists, and more than 3,000 freedmen from New York City in 1783 to transport them to a British colony. Toward this end, Carleton assigned Samuel Birch to create the Book of Negroes.

Seth Warner (May 17, 1743 [O.S. May 6, 1743] – December 26, 1784) was an American soldier. He was a Revolutionary War officer from Vermont who rose to the rank of Continental colonel and was often given the duties of a brigade commander. He is best known for his leadership in the capture of Fort Crown Point, the Battle of Longueuil, the siege of Quebec, the retreat from Canada, and the battles of Hubbardton and Bennington.

Before the war, Warner was a captain in the Green Mountain Boys. He was outlawed by New York but never captured.

Fort Saint-Jean (French pronunciation: [fɔʁ sɛ̃ ʒɑ̃]) is a fort in the Canadian province of Quebec located on the Richelieu River. The fort was first built in 1666 by soldiers of the Carignan-Salières Regiment of France who had travelled to New France to assist the young colony. It was part of a series of forts built along the Richelieu River. Over the years, it was destroyed and rebuilt several times, but it is, after Quebec City, the military site that has been occupied non-stop for the longest time in Canada. The fort is designated as a National Historic Site of Canada, and it currently houses the Royal Military College Saint-Jean. The fort has been continually occupied since 1748, and is the core from which the city of Saint-Jean-sur-Richelieu, Quebec grew around. Fort Saint-Jean played a crucial role in the British defence strategy during the 1775 American invasion of the Province of Quebec.