It's been around a long time, but a major contribution to the worsening of late is the US news media. When my family visited the us in the early 2000s we thought fox news was a parody at first. We could not believe it was being held up as news, when the bias, and outright misinformation was passed off as fact. This platform was used with great effect to seed mistrust in all media, and now it's completely polarised, with most folks refusing to look at certain media sources as they can't be trusted. Other countries regulate the media, news is much closer to fact. News media can and does get sanctioned for any wrong information and have to publicly retract, etc. There are solutions, but the US doesn't want them.

Now social media is here, it's made it a lot worse and more global, but the US had an opportunity in the 90s and 2000s to improve it's media and did not.