Seas Of Venus

In a huge effort, humans terraformed Venus, increasing its reflectivity to reduce its heat absorption, introducing life, and finally introducing people. Just in time because human war created the galaxy's newest star and Venus was all that was left of humanity. The lessons of Earth weren't completely missed. Venus's domed cities (the land areas were considered too dangerous to settle) made plenty of war, but their warfare was limited, civilized, and conducted by professional mercenary companies. Cities who stepped outside of the rules of war could be quickly nuked--a strong incentive toward cooperation. Of course, even 'civilized' warfare is still warfare and mankind's efforts were largely squandered in an entire world that is overrun with mutating and dangerous descendents of the species brought in by Earth's teraformers.
In two linked novellas, author David Drake explores the mercenaries who carry on the wars. In the first, Surface Action, Johnnie Gordon joins his mercenary-uncle Dan Cooke in an attempt to overcome a conspiracy of mercenary companies to preserve their way of life--by preventing Johnnie's father from bringing about a peaceful union of Venus domed cities. With only Dan's mercenary company to protect the young alliance and with multiple opponents lining up, Johnnie's mercenary experience seems doomed. And that's before Dan comes up with a crazy idea involving a cross-country cutting out operation.
In The Jungle, two junior officers face their own failings after their boat is damaged. Each perceives the other as embodying all of the characteristics that they know they are missing themselves--and each uses the other's example for inspiration, subtly living up to the other's misconceptions. But survival is only a part of the requirement. Because the Venus domed cities have themselves reached a critical situation. Somehow, men must reclaim the land while they still have the chance.
In SEAS OF VENUS, David Drake sees the romance of war, but he doesn't let it seduce him. Even distant warfare conducted by professional mercenaries has its costs--including the creation of a self-perpetuating and self-dooming system. The first story, Surface Action, is straightforward, with a twist ending. The Jungle is a continual twist as Drake gives us a deeper insight into the characters and into the world and society which spawned them. The non-linear time flow is occasionally confusing, but the storytelling works.
SEAS OF VENUS. especially The Jungle, is military SF at its best. And Drake's story of a true-life voyage to the jungle of Belize is a nice bonus.