Forgotten Title: Travel Back to Key Events to Prevent Post-Apocalyptic Future

[Chris]

Thanks for reading this post and any help you can provide. This novel began in a post-apocalyptic future with a team of researchers studying key events in history. They were identifying which ones they could alter in order to prevent the tragedy/war which created their present circumstances. Once they identify these events, they travel back in time to alter them. However, they must take great care with what they do, since they have a limited number of jumps.

I think their first attempt is to prevent the assassination of Kennedy, which is successful but doesn't have the desired effect.

I forget what else they tried, but finally, the last woman left on the team decided to travel back to Imperial Russia and convince Catherine the Great that it's imperative for Russia to colonize the west coast of North America.