Answer:
set the US-Canada border at the forty-ninth parallel.
Step-by-step explanation:
A provision of the Treaty of 1818 that expanded the United States also "set the US-Canada border at the forty-ninth parallel."
This is evident in the fact that the Treaty of 1818 often referred to as "the convention respecting fisheries, boundary and the restoration of slaves" broaden the United States. In the treaty, it was certainly written that "the U.S. - Canada border must be set at the 49th parallel."