The Northwest Territorial Imperative was a plan proposed by the United States in the late 1800s. It was a way for the US to gain more land in the western part of the country. The plan was that the US would negotiate agreements with other countries to buy or take over land in the Northwest region of the US. Countries that had land in this area but didn't want to sell it, the US would pressure them to do so, or even threaten military action to take the land. Eventually, this pressure led to the US gaining control of much of the Northwest, including areas of what are now Idaho, Oregon, Washington, and parts of Montana, Wyoming, and British Columbia. This added land helped the US grow and become a much bigger country.