In the 1800's hich country other than the United States claimed part of the Oregon Country?

Answer 1

Great Britain did, as part of Canada. Instead of going to war over it (the slogan was 54-40 or fight, referring to the latitude line at the north end of the Oregon territory), President Polk negotiated with the British to extend the northern border of the US/southern border of Canada from the 49th parallel where it was after the Louisiana Purchase to the Pacific Ocean, only deviating from that to give Canada Vancouver Island.

Answer 2

Who cares!