Using the lure of the Canadian Pacific Railway, a transcontinental line that would unite the nation, Ottawa attracted support in the Maritimes and in British Columbia. In 1866, the Colony of British Columbia and the Colony of Vancouver Island merged into a single Colony of British Columbia. After Rupert's Land was transferred to Canada by Britain in 1870, connecting to the eastern provinces, British Columbia joined Canada in 1871. In 1873, Prince Edward Island joined. Newfoundland—which had no use for a transcontinental railway—voted no in 1869, and did not join Canada until 1949.

In 1873, John A. Macdonald (First Prime Minister of Canada) created the North-West Mounted Police (now the Royal Canadian Mounted Police) to help police the Northwest Territories. Specifically the Mounties were to assert Canadian sovereignty to prevent possible American encroachments into the area. The Mounties' first large-scale mission was to suppress the second independence movement by Manitoba's Métis, a mixed-blood people of joint First Nations and European descent, who originated in the mid-17th century. The desire for independence erupted in the Red River Rebellion in 1869 and the later North-West Rebellion in 1885 led by Louis Riel.