I. The international airport serving the capital of Montenegro has only two arrival gates, and last spring they were busier than usual. I was there for the same reason many others were: The tiny Balkan state had become the unlikely center of a mostly American social and political movement. Specifically, I had come to observe Zuzalu, a two-month co-living experiment that had been organized—and to some extent paid for—by Vitalik Buterin, a co-founder of the eco-friendly cryptocurrency ethereum. It was being hosted at a new resort and planned community on the Adriatic coast, not far from the village of Radovići. Part retreat and part conference, it was also a dry run for the more permanent relocation of tech-industry digital nomads to different parts of the world, where they could start their own societies and design them to their liking. Some 200 people had signed up for the full two months. Others, like me, popped in and out. The slate of talks for the days I was there was titled “New Cities and Network States.” European …