You could base a campaign on the Time Wars series by Simon Hawke (https://www.goodreads.com/series/44458-timewars). You play a small squad of time soldiers going back in time to fix things that a rogue group of time terrorist are committing.
Later in the series two divergent timelines are at war with each other trying to wipe out the other. (Either way they are a fun read.)
goodreads.com – The Ivanhoe Gambit (Time Wars, #1)