Originally Posted by
Friv
entire swathes of time were wiped out of existence, thrown into nightmarish repeating paradoxes, doubled-up on each other, and so on. The war only ended when the Doctor obliterated both species entirely from the timeline, undoing most of the damage that they did.
I think that's about as powerful as time travel can get before it moves into the "infinite capability" zone, honestly; you can make whatever changes you like, but if you make the wrong ones you blow up everyone you were trying to save. Of course, if your goal is the eradication of every other universe, blowing up their universe while making alterations to it isn't such a net problem.