In the American Revolutionary War units of the Continental Army were assigned to any one of seven regional or territorial departments to decentralize their command and administration. This was necessary because the regiment was the largest permanent unit in the Continental Army. A superior headquarters, above regiment, was needed if more than a few regiments were stationed in the same department. Although brigades, divisions, and field armies existed, they were temporary units which did not necessarily include all the units assigned to a department. Nor did field armies include establishments of the staff, such as magazines (supply depots) of the Quartermaster General's Department, or hospitals of the Hospital Department. The militia in a department was usually at the disposal of the department commander.
Departmental organization
The Continental troops in a department constituted its garrison. If the garrison was sufficiently large, the units might be assembled into a field army. In this case the commander of the territorial department and the commander of the field army would be one and the same officer. Thus, the commanding general of the Northern Department was also commanding general of the Northern Army, and the commanding general of the Southern Department was also commanding general of the Southern Army. Armies did not, however, invariably receive a geographical designation. Because the field army under Washington's personal command contained the majority of Continental Army units it was designated the Main Army. Each department had a semi-autonomous commanding officer, usually a commanding general, under the overall command of Washington as General and Commander-in-Chief. The Continental Congress dealt with and through the department commanders.
Appointment of department commanders
Throughout the war, the Continental Congress retained exclusive authority to appoint or remove department commanders. In practice, when an urgent need arose, a temporary commander was just as frequently appointed by George Washington or the executive power of one of the states, pending the approval of the Continental Congress. Many of these temporary department commanders were then confirmed and formally appointed by the Congress. This practice, along with control of the Continental Army and Navy through the war and marine committees of the Continental Congress, established the precedent for civil control of military affairs later embodied in the Articles of Confederation and the United States Constitution.
Relations between the departments and the states
The department commanders and their staffs also worked directly with the governments of the states within their department. At first these were the ad hoc provisional governments developed in 1774 and 1775, but the practice continued after 1776 when the states replaced their Provincial Congresses and Conventions with permanent governments operating under written constitutions. Ordinarily departments were commanded by major generals. Washington as a full general was the ranking general officer in the Continental Army throughout the war.
Departments
In general there were seven territorial departments, although their boundaries were subject to change and they were not all in existence throughout the war.
Canadian Department
The establishment of the Canadian Department reflected the aspirations of the Continental Congress and some Americans to annex the British province of Quebec, then often referred to as "Canada", but the effort was ultimately unsuccessful. Although the Americans captured Montreal in November 1775, and established their headquarters at Château Ramezay, the region was never entirely under the control of the Continental Army. The Canadian Department was formally established from the New York Department on January 17, 1776. After the Invasion of Canada failed, all troops were withdrawn to Fort Ticonderoga, New York. The Canadian Department was officially discontinued on July 8, 1776.