It's almost impossible to overstate how significantly social media altered the fabric of the Internet. From "on the Internet, nobody knows you're a dog" to everybody having seen multiple photos of your dog. From a decentralized web of special-interest fiefdoms to digital sharecropping.

And now, the era of social media is over. Instagram's death leaves Twitter as the last relevant social network, and Twitter's prospects don't look too rosy these days either.

The fourth era of the Internet appears to be content distribution platforms serving a large audience that passively consumes the content of (or, at best, interacts parasocially with) a small cadre of creators. The digital frontier has been fully settled and it now looks an awful lot like the old country.