If You Could Change One Historic Event Which One Would It Be?

I wish the US (and the rest of the west) and the USSR would have become strong allies after WW2 instead of seeing each other as existential threats. I think World War 2 was kind of an important maturing point for the possibility of peace. I think trying to prevent it would only cause other war at another time.

As allies, a lot of the various proxy wars would not have happened. Not seeing each other as ideological threats would mean more collaboration and trade between the entities. The economic warfare between the two sides would not have happened and we could better see the economic models play out to their more natural conclusions.

I think it would have set us up for an even more peaceful world today and possibly a real chance at a united global federation at some point. (Let's get that precursor to Starfleet going already)