The North-Western Territory was a region of British North America until 1870. Named for where it lay in relation to Rupert's Land, the territory at its greatest extent covered what is now Yukon, mainland Northwest Territories, northwestern mainland Nunavut, northwestern Saskatchewan, northern Alberta and northern British Columbia. Some of this area was originally part of Rupert's Land due to inaccurate maps. The acquisition of Rupert's Land was the largest land purchase in Canada's history.