Choas is kinda funny. When you have systems of a large number of non-linear things they tend to average out. A time traveler could be as little as a single part

Choas is kinda funny. When you have systems of a large number of non-linear things they tend to average out. A time traveler could be as little as a single particle and still re-shuffle the entire deck so to speak. But it's still the same deck of cards. In the end you're still in nearly identical initial conditions. While the individuals will change, the whole of society will be extremely similar due to statistical mechanics. Susie being slightly more aggressive will be balanced out by Johnny being slightly less aggressive, etc... You may cause a new extrema event though like Johnny inventing a cheap nuclear bomb, or you may prevent one. A good time traveler would be able to sit outside time and probe reality using tiny changes until they get the outcome they want. But at that point you are so powerful I can't imagine anyone would care. Maybe that's why we didn't all kill ourselves yet. Some time traveler poking at the timeline.