Complex sentence: Mary was the first generation of one of the main families of what is referred to as the Métis people, the offspring of European men who married Native American women, who played a major role in the 19th century fur trade in Missouri and Kansas.
Split into simpler sentences: Mary was the first generation of one of the main families of what is referred to as the Métis people, the offspring of European men who married Native American women. They played a major role in the 19th century fur trade in Missouri and Kansas.