Answer
Failure marked St. Clair's primary invasion in 1791. The expedition, aimed at quelling Native American resistance in the Northwest Territory, ended in disaster. Native American forces ambushed and annihilated St. Clair's army, leading to the loss of over 600 soldiers and the abandonment of the campaign. This defeat significantly weakened the United States' position in the region and delayed the establishment of American control over the Northwest Territory.