Complex sentence: He entered the employ of the Hudson's Bay Company as a fur trader and in 1792 completed his first significant survey, mapping a route to Lake Athabasca (where today's Alberta/Saskatchewan border is located).
Split into simpler sentences: He entered the employ of the Hudson's Bay Company as a fur trader. In 1792 he completed his first significant survey, mapping a route to Lake Athabasca (where today's Alberta/Saskatchewan border is located).