The Nez Perce Chief Who Refused To Surrender 40 Miles From Canada — Then Slipped Past The Army And Escaped
The international boundary between the United States and Canada — the 49th parallel — had been formalized in 1818 for the territory east of the Rockies and extended to the Pacific in 1846.
By 1877, it had been surveyed across most of the northern plains.
Indigenous people on both sides of the line had been crossing it since before it existed, as the movement of the plains peoples did not respect boundaries that had no physical reality.
But by 1877, the line had acquired specific political meaning: American soldiers could not legally cross it in pursuit of Indigenous people.
This had been demonstrated with the Lakota after the Little Bighorn.