Want Economic Growth? Try Urban Density

Here's a big economic and political thesis: The U.S. has run out of frontiers, both literal and figurative. At first, growth was fueled by expansion into the West, use of natural resources and the build-out of national infrastructure. In the early- and mid-20th century, an unprecedented explosion of new technologies -- electricity, automobiles, airplanes and others -- opened up the suburbs, which acted like a new frontier. More recently, the Internet and globalization, especially China, were frontiers that gave the economy yet more room to expand.

But these growth opportunities may now be running out. Information technology is improving our lives by giving us more fun things to do with our leisure time, but it isn't providing the kind of productivity boost gained from previous technological revolutions. And the heyday of expansion into China may be over, given that country’s economic slowdown, its decreasing openness to Western companies and the broader slump in world trade.