Complex sentence: He seems dedicated to brokering a peaceful agreement between the Earthrace and the Moonrace, and to building up the Earth Militia in case talks fall through, but he is motivated by personal ambition rather than the welfare of his people.
Split into simpler sentences: He seems dedicated to brokering a peaceful agreement between the Terrans and the Moonrace, and to building up the Earth Militia in case those talks fall through. Unfortunately, Guin is motivated by personal ambition rather than the welfare of his people.