Very insightful observation. Where did these polarization come from?

I suspect the external factors are that the environment and the global order are both strained to near collapse. There are now less resources, less time, and less options, but too much blame to spread around.

These external pressures lead to changes in internal attitudes. The idea that we all want the same thing but just taking different paths to get there is giving way to the idea that we want different things. This is because when you have less time and resources, different paths' claim on those resources can limit your own claim and undermine your chances of success. Peace and harmony come from abundance; war and strife from scarcity.

And then enter politics that mobilize people into opposite camps in order to grab power, and companies who create echo chambers to make money, and we now have spiralling vicious circles.