Fifty years ago Saturday, under the cover of darkness on Aug. 13, East Germany broke ground on the Berlin Wall, which became one of the most iconic symbols of violence and exclusion the world has ever known.

When the Berlin Wall fell in 1989, images broadcast around the world of Germans climbing the wall and dancing together before they began tearing it down piece by piece marked the rapid decline of Soviet-style communism. It also raised hopes that a new borderless world of democracy and globalization was dawning.

In the 22 years since the fall of the Berlin Wall, 28 new border walls have been constructed around the world, making the hope of a borderless world seem quaint. For comparison, in the 44-year period from the end of World War II until the fall of the Berlin Wall only 11 border barriers were built. Furthermore, while the Berlin Wall was built by a totalitarian regime to keep people in who wanted to cross a border in search of freedom and economic opportunities, these new border walls were built by leading democracies including the United States, the European Union and India in order to keep people out who are seeking freedom and economic opportunities.

The hardening of borders in recent years is often linked to the threat of terrorism, but the impact has largely been on poor migrants seeking a better life. Although terrorism is used to justify some of the new walls, the strongest indicator of whether a country will build a barrier is whether it shares a border with a substantially poorer neighbor. The average per capita gross domestic product (in 2010 U.S. dollars) of the countries that built walls after the fall of the Berlin Wall is $14,067, while the average of the countries on the other side is only $2,801.

Although the predicted borderless world did not come into being, the purpose of political borders has changed in the era of globalization. Historically, most political borders were defensive lines where the army of one country prevented the movement of the army of another.

After the creation of the United Nations, which requires in its charter that all member states respect the sovereignty and territorial integrity (read "borders") of all other members, borders were transformed into the lines that separated different systems of legal, economic and political practices.

Expensive border fences and walls are not necessary for either of these purposes. They do not stop the missiles or fighter jets of an invading army, nor are they any better than a map at representing the edges of different legal or political systems. However, border walls are relatively effective at preventing the movement of actual people.

People in poor or repressive societies, who are increasingly aware that people elsewhere live much more privileged lives than their own, are encouraged to take advantage of the new economic and social opportunities of globalization as long as they remain within the borders in which they were born. People in Bangladesh are encouraged to live the dream of globalization by working in a new factory, but not by moving to another country where they would be paid more for doing the same work. People in Zimbabwe who dream of freedom are encouraged to do everything they can in pursuit of democracy, except moving their family to place where democracy already exists.

The enduring legacy of the Berlin Wall is not the inspiring notion that freedom and the will of the people can knock down a wall. Instead, the lesson learned is that border walls — particularly those supported by large deployments of border guards — are relatively effective at preventing the movement of poor people. Consequently, rather than the completely borderless world imagined in 1989, we live in a world that is connected economically and socially, but also increasingly divided territorially by more walls that are taller, longer and stronger than the Berlin Wall ever was.