Which territory was claimed by both the U.S. and Britain, leading to joint occupation?

The Oregon Territory was claimed by both the United States and Britain, leading to a period of joint occupation from 1818 until the Oregon Treaty in 1846. This territory was highly sought after due to its fertile land and resources, and both nations had interests in its settlement and use. The joint occupation allowed for coexistence, where settlers from both countries could live and establish communities. The dispute over this territory was driven by the phrase "54°40' or Fight!" which referred to a claimed northern boundary. Ultimately, this territorial claim was resolved through diplomacy, and the Oregon Treaty established the current U.S.-Canada border along the 49th parallel. The question highlights an important aspect of U.S. territorial expansion and the complexities of international negotiations during the 19th century.