The Makaum War2 books in series
Master Sergeant Publisher's Summary
They call it The Green Hell. A maze of tangled jungle, the planet Makaum is one of the most dangerous places in the universe. And for Terran Military Master Sergeant Frank Sage, it is now home.The war between the Terrans and the Phrenorians rages, and both sides have their sights set on Makaum. If the planet's rich resources fall into enemy hands, it could mean devastation for the Terran army. To ensure that doesn't happen, Sage is sent to assess the Makaum troops and bring them in line with Terran military standards.
But soon after arriving at his post, he realizes that the Phrenorians are not the only threat. Heading up a small but fearless unit, Sage must stop a brewing civil war with the power to unleash a galactic cataclysm unlike anything ever seen.