Complex sentence: It showed up in the interior trading posts of the Hudson's Bay Company in 1782, and then it devastated the people of the Great Plains during the 1837-38 smallpox epidemic.
Split into simpler sentences: It showed up in the interior trading posts of the Hudson's Bay Company in 1782. It was followed a generation later by a second epidemic that devastated the people of the Great Plains during the 1837-38 smallpox epidemic.