At what point did liberal/conservative become...

I think a lot of the divide is media driven/ fueled...and not just talk radio or Fox News, although that's a part. The internet plays a huge role. Everything from social media to blogs to internet news sites to message boards like this. The internet has allowed us to share and express our opinions, outrage and ignorance in unprecedented ways. In past times, we actually had to engage people in person, or write a letter to the editor. The internet, and to some degree, the news media has expanded and emboldened our political conversations. We can be anonymous, or nearly so. We can say hateful or hurtful things to others without fear of it ruining our relationships (although in many cases, it does, and has ruined friendships and family harmony).