Complex sentence: He and his brothers had been given native names upon their first meeting with Cheyenne in the area, which had been a convivial occasion during which their respect for the Cheyenne protocols had set a firm base for their future development of the fort and trading.
Split into simpler sentences: He and his brothers had been given native names upon their first meeting with Cheyenne in the area. Their respect for the Cheyenne protocols during the convivial occasion set a base for their future development of the fort and trading.