I think the humans have been dividing themselves up into tribes for a long time. While technology isn't completely blameless, Technology does provide another avenue where humans establish and patrol boundaries via social cues. And those cues can maybe be magnified by tech and exploited by political parties on both sides.

I found this podcast particularly interesting (though maybe not 100% correct), but it discusses interesting urban/rural social and cultural boundaries. And I think it's fairly perceptive in the observation that completely unrelated political issues are bound together simply because they happened to fall on different sides of that cultural divide. I think that divide had formed long before the internet and certainly social media.

It was also recorded just before the election which additionally makes for some prophetic elements.

Cracked Podcast #148 http://www.earwolf.com/episode/trump-country/