In 1775, on the eve of the American Revolution, the British Empire included 20 territories in the Western Hemisphere northeast of New Spain. These colonies were:
Britain had acquired Quebec from France and East and West Florida from Spain by the Treaty of Paris (1763), which ended the Seven Years' War.
The United States of America, upon acknowledgement of their sovereignty, acquired the part of Quebec south of the Great Lakes by the Treaty of Paris (1783); at the same time Spain gained West Florida and regained East Florida.
Nova Scotia was split into modern-day Nova Scotia and New Brunswick in 1784. The part of Quebec retained after 1783 was split into the primarily French-speaking Lower Canada and the primarily English-speaking Upper Canada in 1791.
After the War of 1812, the Treaty of 1818 established the 49th parallel as the United States–British North America border from Rupert's Land west to the Rocky Mountains. Britain gave up Oregon south of the 49th parallel, which was part of the Hudson's Bay Company's Columbia District, under the Oregon Treaty of 1846.
The boundary of British North America with Maine was clarified by the Webster-Ashburton Treaty of 1842.
The Canadas were united into the Province of Canada in 1841.
On 1 July 1867, in an action known as Confederation, an act of the British Parliament called the British North America Act formed the Dominion of Canada from the Province of Canada, New Brunswick, and Nova Scotia. The former Province of Canada was split back into its pre-1841 parts, with Canada East (Lower Canada) renamed Quebec, and Canada West (Upper Canada) renamed Ontario. These were the original four provinces of Canada.
In 1870, Rupert's Land was annexed to Canada as the Northwest Territories (NWT) and the new province of Manitoba. British Columbia, the British colony on the west coast north of the 49th parallel, joined as Canada's sixth province in 1871, and Prince Edward Island joined in 1873. The boundary of British Columbia with Washington Territory was settled by arbitration in 1872, and with Alaska by arbitration in 1903.
The Arctic Archipelago was ceded by Britain to Canada in 1880 and added to the Northwest Territories. Subsequently, large sections of the NWT were split off as new territories (Yukon, 1898; Nunavut, 1999) or provinces (Alberta and Saskatchewan, both in 1905), or were added to existing provinces (Manitoba, Ontario, and Quebec, in stages ending in 1912).
In 1907 the sole remaining British North American colony, Newfoundland, was granted dominion status, although starting in 1934 it returned to British administration under the Commission of Government. In 1949 the island of Newfoundland, and its associated mainland territory of Labrador, joined Canada as the tenth province.
Although semi-independent from 1867, and fully sovereign on foreign affairs with the Statute of Westminster 1931, the last vestiges of Canada's constitutional dependency upon Britain remained until Canadians agreed on an internal procedure for amending the Canadian Constitution. This agreement was implemented when the British Parliament passed the Constitution Act of 1982 at the request of Parliament of Canada.