I want to create a story where an alien had the power to telepathcally control the collective choices of human society (example controling how we feel about certain events , morals and political beliefs)
For unknown reasons this alien saw human civilization as a threat to his own existence.
How would this alien go about strategically using his telepathic powers to covertly destroy society until human civilization eventually collapses?
It is actually easier than you think, you don't have to control too many humans to get us into an apocalyptic war, Just pinpoint a few world-leaders and they will get the things sorted out for you.
Step 1: Select a few nations that are powerful and are usually against each other. (US, China, Russia for starters).
Step 2: Select the political leaders (just the top ones), some influential media houses, and the intelligence agencies.
Step 3: Make them feel like the enemy are at the gates (not literally) and are about the launch of an all-out attack.
Step 4: A few false memories here and there, a few accidents at key locations (like a distant air-base), a missing nuclear submarine should do the trick.
Step 5: Just relax, our leaders will do the rest for you, But don't forget to make minor adjustments if and when required.
Step 6: Come for cleanup of whatever left when its all over.
To be honest, the most terrifying part of this answer is that i can't say it isn't happening right now, but to answer your question:
Take control of the media, both sides: if you control the media you control what most of the population knows and feels, so from there is trivial to make an ideological war between them so people will get at each other throats.
Take control over some key people in different countries: mostly high level politicians, but public figures, celebrities, whistle-blowers and tech-owners are a good start. With so many different angles of attack you can cause some real damage, including but not limited to:
If this answer hit too close to home you can always dismiss it and go with something more fictional like WWW3 or something
I'd assume that the aliens can control any number of people, from one to the global population, so here some ideas, roughly ordered by time frame
Just convince all the human race (or at lease, a good 80% of them) that they need to commit a ritual suicide at a certain date for whatever reason you want. In this case the collapse is basically immediate.
As the previous but just convince a small percentage about 2-3% to commit ritual suicide every single day. About 70/210 millions (random) people will kill themselves every day. Given that the population grow at about 1% a year, this means that in a week you go back about 10 year in population numbers, without the time to adjust the society, which likely will collapse in about a month (or a couple) if not for anything else because there will be not enough people with the skill to maintain the current infrastructure.
Another way it to make everyone extremely suspicious (or even better, extremely paranoid) about everyone else. The current society works on the the implicit trust between people. Remove this trust and the society will likely collapse since it is needed for everyday activity: are you really sure that the guy who is selling you the food does not want to poison you ? Or the bus driver does not want to kill all the passenger ? And so on...
Exploit what you already have. Make people follow and to believe to every conspiracy thesis you can think of. Pretty soon you will see that the infrastructure will be damaged from someone (COVID-19 and 5G tower for example). Once the infrastructure begin to fall, and it will fall because the people who want to destroy it are way more than the people who repair it, the society cannot sustain itself to the current level and begin to fall too.
