Undying mercenaries is pretty good..
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From Book 1: In the twentieth century Earth sent probes, transmissions and welcoming messages to the stars. Unfortunately, someone noticed.
The Galactics arrived with their battle fleet in 2052. Rather than being exterminated under a barrage of hell-burners, Earth joined their vast Empire. Swearing allegiance to our distant alien overlords wasn’t the only requirement for survival. We also had to have something of value to trade, something that neighboring planets would pay their hard-earned credits to buy. As most of the local worlds were too civilized to have a proper army, the only valuable service Earth could provide came in the form of soldiers…someone had to do their dirty work for them, their fighting and dying.
I, James McGill, was born in 2099 on the fringe of the galaxy. When Hegemony Financial denied my loan applications, I was kicked out of the university and I turned to the stars. My first campaign involved the invasion of a mineral-rich planet called Cancri-9, better known as Steel World. The attack didn’t go well, and now Earth has entered a grim struggle for survival.
Humanity’s mercenary legions go to war in STEEL WORLD, bestselling author B. V. Larson’s latest science fiction novel.
I enjoyed Frontlines as well.
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The year is 2108, and the North American Commonwealth is bursting at the seams. For welfare rats like Andrew Grayson, there are only two ways out of the crime-ridden and filthy welfare tenements: You can hope to win the lottery and draw a ticket on a colony ship settling off-world . . . or you can join the service.
With the colony lottery a pipe dream, Andrew chooses to enlist in the armed forces for a shot at real food, a retirement bonus, and maybe a ticket off Earth. But as he starts a career of supposed privilege, he soon learns that the good food and decent health care come at a steep price . . . and that the settled galaxy holds far greater dangers than military bureaucrats or the gangs that rule the slums.
The debut novel from Marko Kloos, Terms of Enlistment is an addition to the great military sci-fi tradition of Robert Heinlein, Joe Haldeman, and John Scalzi.
We are Bob, We are Legion is unique and I don't think I've read anything similar.