Orphan's Alliance by Robert Buettner
Humans have been discovered on the Outworlds. And the Army decides to send emissaries. Emissaries like Jason Wander. As intraplanetary conflicts rage around him, and the personal stakes get ever higher, Jason finds that playing planet-hopping politician can be harder than commanding armies. When united mankind squares off to battle the Slugs for a precious interstellar crossroad, Jason will discover that the most dangerous enemy may be the one he least expects.