also Psychohistory would be invalid with time travel.
Asimov did the opposite of time travel back with psychohistory: he had the civilisation changes predicted and by that could intervene with his specialist community to shorten the dark ages to get back to the "good" imperium in a much shorter time.
He believed well chosen interventions would matter.
My take out as concept is that mass scale changes of civilisation are what they are: mass scale forcing effects from averages and common denominators.
And specific interventions only influencing when they influence succesfully the mindsets of the masses.
Looking back at those specific changes the last centuries, most of them were techs, technical inventions. And they are once Science/Engineering was freed, autonome and close to unstoppable.
Going backward in time: when Kennedy won from Nixon. Was that not that TV debate that made the difference ? Kennedy's confident and charming presence into every household livingroom. The TV changed rapidly over time from info to more entertainment, and politicians had to be better in PR. That changed the properties needed for politics and therefore the kind of politics.
Going back further in time with a media tech: when the radio was developed (WW1 important) mass influence became possible to all citizens of a nation. The societal development of increased individual freedom, the need for cohesion back, the need for guidance to unity. And there it was: Mussolini had the radio available to reach with his speeches all citizens, also in the many smaller villages of Italy. Hitler's demagogue speeches to mass manifestations, also on the radio... all citizens united in those moments.
Going back further in time with a media tech: The printing press. Written manuscripts were expensive and for the Church, the academia and the rich. The rate of them in regions coupled to the rate of urbanisation in those regions. The printing press changed that accessability. Not only for the Bible, knowledge and philosophy, but starting in the 16th century also as mass media by pamphlets, first mostly on religious topics infighting. Those pamphlets had a much bigger reach than just the bigger cities.
When William embarked to the UK for the Glorious Revolution, he had with him mobile printing presses, and used them for printing his propaganda pamphlets, tuned to the latest development all the time.
And now we have social media and internet, connecting everybody to everybody, and cyber intelligence and cyber influencing in a rapid.
This simple set of media techs, printing press, radio, TV, internet, social media, their technical development autonome and unstoppable, have changed imo much more than the individual specifics of this or that politician.
I think that techs are the real driving factor, and CIVs are a follower. And currently the speed of techs is much higher than our cultural answers with CIVs.
As much in or out of control as when you are white water rafting.
Once the tech agricultural was developed, we were in the rollercoaster of techs.
At the start the techs went slowly and were still coupled to the individual CIV's. Astronomy here, the wheel there, etc. The Roman Catholic Church for a while an inhibitor of some Science insights and therefore techs.
But with our globalisation of tech exchange, anything developed anywhere is rapidly everywhere for the masses.
This was in fact my take out from the Foundation Trilogy: Influencing anything, like changing history, happens by influencing the masses. The more democratic societies are, the more masses matter. The more consumeristic civilisations are, the more masses matter.
That leaves less room for pinpoint changes by changing individuals in powerful positions. For every Marie le Pen, there is another.
