The Martian Marauders. Jack Commer, Supreme Commander, #1

Inexplicable solar system disasters confound humanity as the outer planets explode and asteroids are thrown into the sun. These horrors force the development of the United System Space Force and a panicky acceleration of space technology and weaponry. But human conflict accelerates even after Mars exploration and the discovery of Star Drive, and the USSF renders the Earth uninhabitable when Captain Jack Commer drops the planet-wrecking Xon bomb to end the Final War.
The remnants of Earth's population hastily evacuate to Mars, but somehow the USSF has overlooked an intelligent race on Mars which is extremely displeased at the arrival of two billion shellshocked humans. Soon native Martians rise in rebellion, led by their treasonous human emperor. Jack and his three brothers are sent into the deep desert to battle Martian insurgents armed with shatterguns that crack their victims into millions of jagged pieces of glass.
Then Jack compromises the entire mission when he falls in love with the Martian emperor's beautiful brainwashed consort.