Jefferson instructed Lewis and Clark to make peace with all tribes they encountered and to assert American authority. The Corps would introduce themselves with a uniformed parade, a few gunshots, a demonstration of modern marvels (such as the magnifying glass and the air gun), and a speech: “The President,” Lewis would say, “is now your only great father.... he will serve you, & not deceive you”

But disobey him and he “could consume you as the fire consumes the grass of the plains.” After the speech came presents—often medals with two hands clasping on one side and Jefferson’s likeness on the other. In July 1806, after a rare skirmish, Lewis placed one of these “peace” medals on a Blackfeet corpse “that they might be informed who we were.”