Let me play devil's advocate for a moment:
Is there any hard data that proves that people are becoming increasingly tribal?
Perhaps the number of radicals is the same like it was 20 years ago, but the internet and social media now give those radicals a voice. Because of this it feels like we are becoming increasingly tribal, when in reality we're not.
Similar to how the crime rates are going down, but most folks think that it's getting worse.
For us who spend a large portion of our time on internet, it certainly feels like everything is crashing down.