Tim Marshall, the New York Times bestselling author of Prisoners of Geography, analyzes the most urgent and tenacious topics in global politics and international relations by examining the borders, walls, and boundaries that divide countries and their populations.
The globe has always been a world of walls, from the Great Wall of China to Hadrian's Wall to the Berlin Wall. But a new age of isolationism and economic nationalism is upon us, visible not just in Trump's obsession with building a wall on the Mexico border or in Britain's Brexit vote but in many other places as well. China has the great Firewall, holding back Western culture. Europe's countries are walling themselves against immigrants, terrorism, and currency issues. South Africa has heavily gated communities, and massive walls or fences separate people in the Middle East, Korea, Sudan, India, and other places around the world.

In fact, at least sixty-five countries, more than a third of...