I have been trying to track down story I read in a middle school or high school class about a decade ago. It involves a soldier that was sent to "the end of time" in a gigantic battle for the universe. All of the soldiers in the battle get cybernetic enhancements to aid in their fighting ability. That was just the main character's back story. The main part had to do with the soldier coming home or to a comfortable time and trying to live in peace, but he spots a group of soldiers also from the war that start causing trouble in his town and so he fights them to protect the locals. I appreciate any help. I don't know why but occasionally i think of that story and have tried to track it down a few times, obviously to no avail.
Sounds like "A Dry, Quiet War" by Tony Daniel, 1996 (full text here) as previously asked here a few other times. The protagonist is Col. Henry Bone, a veteran of the "Big War at the End of Time." The bad guys are "glims":
"Soldiers who don't go home after the war. The fighting gets into them and they don't want to give it up, or can't. Sometimes they have ... modifications that won't let them give it up. They wander the timeways—and since they don't belong to the time they show up in, they're hard to kill. In the early times, where people don't know about the war, or have only heard rumors of it, they had lots of names. Vampires. Hagamonsters. Zombies."
Here's a reference to DavidW's comments about the cost to the protagonist for intervening:
"You're some bigwig, ain't you, skyfaller? Somebody that matters to the outcome," Marek said. "This is your actual and you don't want to fuck yourself up-time so you won't fight." He smiled crookedly. A diagonal of teeth, straight and narrow, showed whitely.
(I only know the story through this site; I re-found it by searching the story-identification archives for "veteran")