Complex sentence: The North West Company established the area its regional headquarters and soon Grand Portage became one of Britain's four main fur trading posts, along with Niagara, Detroit, and Michilimackinac.
Split into simpler sentences: The North West Company established the area as its regional headquarters. Soon Grand Portage became one of Britain's four main fur trading posts, along with Niagara, Detroit, and Michilimackinac.