I want out of this outfit
Military SF has its own set of cliches, but I really enjoy it, especially anything by David Weber. His Honor Harrington series really epitomized the genre, as far as I'm concerned. Crusade had an interesting premise: a group of colonists were forced to flee an Orion (the race humanity was fighting a war with at the time) through a blind warp point, a point that no survey ship had ever escaped from. There, they met a pre-technological society and "uplifted" them, to use David Brin's term. Ninety years later, when men and Orions were allies, they emerge from the jump point ready to make jihad on the enemies of Holy Mother Terra. Lo and behold, men had fallen under the influence of the "satan-Khan" and were in a state of apostasy. So you got it, time to make a crusade to free Terra...from the humans.

That said, all of the battles they fought were extremely bloody. Because (usually) the only way into a system was by a known jump point, ships could be fired upon by fixed emplacements almost immediately. Losses in the first waves often approached 100%. Dozens of battlecruisers and dreadnaughts might be lost in minutes. That's no way to fight a war.