Complex sentence: A fur-trading settlement quickly grew at the crossroads that straddled the banks of the river, the center of a trading route of that extended from Montreal to the Sault, and from the Sault to the country north of Lake Superior.
Split into simpler sentences: A fur-trading settlement quickly grew at the crossroads that straddled the banks of the river. It was the center of a trading route of that extended from Montreal to the Sault, and from the Sault to the country north of Lake Superior.