Complex sentence: The North West Company sent a French-Canadian, François-Firmin Boucher, to speak to Semple's men, and he and Semple argued, and a gunfight ensued when the English tried to arrest Boucher and seize his horse.
Split into simpler sentences: The North West Company sent a French-Canadian, François-Firmin Boucher, to speak to Semple's men. He and Semple argued, and a gunfight ensued when the English tried to arrest Boucher and seize his horse.