The Blackfeet were the strongest military power on the northwestern plains in the historic buffalo days. For half a century up to 1805, they were almost constantly at war with the Shoshonis and came very close to exterminating that tribe. They aggressively asserted themselves against the Flatheads and the Kutenais, shoving them westward across the Rockies. They got on fairly well with English and Canadian traders during the heyday of the fur trade on the Saskatchewan River, but on the upper Missouri they took an early dislike to Americans, whom they called "Big Knives." American fur traders, such as Manuel Lisa, Pierre Menard, and Andrew Henry, were literally chased out of Montana by the Blackfeet.