There were some episodes of StarTrek, that showed the Federation had a time travel branch - with their own ships, which were capable of altering the time line. Of course, that never turned out well. lol
There was a video game I used to play, Red Alert 3 (I believe) where the prior games were based around US vs USSR war ... and the losing USSR invented time travel to kill Einstein, so they could win the war. The unexpected consequence was that while the US and USSR were fighting, the Empire of Japan built their forces and attacked when both the US and USSR were weakened.
Plenty of time travel stories where the moral is - beware of unintended consequences. lol