Complex sentence: Section I. Captain William Stairs was appointed to lead the expedition, since he had served as Stanley's second in command on the Emin Pasha Relief Expedition and had a reputation of someone who would obey orders and get the job done.
Split into simpler sentences: Section I. Captain William Stairs was appointed to lead the expedition, on the basis of his experience on the Emin Pasha Relief Expedition on which he had become Stanley's second in command. He had a reputation of someone who would obey orders and get the job done.