Accessible only by car via miles of winding, dusty Croatian roads, Gornja Siga – current population zero – is an unlikely testing ground for a plan to shape the world’s political future. It is a secluded area where verdant forest meets white sand on a western bank of the river Danube. The only signs of life are a single dilapidated building with a curious flag flying outside, pheasants, deer, the occasional wild boar, and eagles and falcons overhead. Yet last Monday the Eurosceptic Czech politician Vit Jedlicka and two other libertarians declared this 7 sq km of Serbo-Croat no-man’s-land the...