I don't believe anyone thinks this is a completely new addition to the human psyche (i.e. people weren't tribal before for internet), only that the changing online landscape has made it more visible, easier to take part it, and increased the number of 'battlegrounds' for this behaviour to take place. This has probably a fair amount to do with the increasing 'social integration' of the internet, as well as the increasing ease of access, as well as other reasons.
Within the lifetime of many (most?) of its users, the internet has changed from something with a primary focus on 'information' and relatively difficult to access (families might have one internet connected computer per household), to something that many people have immediate access to anywhere just by reaching into their pockets.
I doubt many would say the behaviours visible now are 100% 'new'. People have been tribal ever since we had tribes. But you'd be overlooking an awful lot to say "nothing has changed".