Cambridge Analytica was a company that used machine learning algos on Facebook user data to target hyper-specific political propaganda to many small segments of voters, rather than few large segments. They spent years testing and refining their process in the developing world in preparation for deployment in the West.

Steve Bannon was the VP. As soon as they pulled off Brexit, he left to head up Trump’s campaign using the same techniques.

https://en.m.wikipedia.org/wiki/Cambridge_Analytica

To add to what others are saying, I'd recommend taking a look at the documentary The Great Hack.