Who established the 49th parallel?

The 49th parallel was established as a boundary between the United States and British North America through the Oregon Treaty of 1846. This treaty was negotiated between the United States and the United Kingdom, primarily driven by U.S. expansionist interests and the desire to resolve territorial disputes in the Pacific Northwest. The boundary runs west from the Lake of the Woods to the Pacific Ocean, effectively defining much of the current U.S.-Canada border.