Subject of trade that gave rise to St. Louis and Detroit

FUR

This valuable commodity was heavily trapped by French explorers in the 17th and 18th centuries, often exchanged for tools and weapons with Indigenous peoples. Think warm, luxurious, and wild.

This clue points to "FUR" because both St. Louis and Detroit were founded as key trading posts in the North American fur trade. In the 17th and 18th centuries, fur—especially beaver pelts—was a major commodity that drove exploration and settlement in the region. The word "trade" in the clue hints at the economic activity that made these cities important, while "subject" simply refers to the item being traded.