The Berlin Wall wasn't the only barrier to fall after the collapse of the Soviet Union and the end of the Cold War. Traditional barriers to the flow of money, trade, people and ideas also fell.
Americans have so far put up with inequality because they felt they could change their status. They didn't mind others being rich, as long as they had a path to move up as well. The American Dream is all about social mobility in a sense - the idea that anyone can make it.
If there is one lesson for U.S. foreign policy from the past 10 years, it is surely that military intervention can seem simple but is in fact a complex affair with the potential for unintended consequences.
During the Cold War, we were interested because we were scared that Russia and the United States were going to go to war. We were scared that Russia was going to take over the world. Every country became a battleground.
In a world awash in debt, power shifts to creditors.
What we see today is an American economy that has boomed because of policies and developments of the 1950s and '60s: the interstate-highway system, massive funding for science and technology, a public-education system that was the envy of the world and generous immigration policies.
Conservatives used to believe in confronting hard truths, not succumbing to comforting fairy tales. Some still do.
The United States is going to be a rich country, it is going to be prosperous, but it is not going to be able to take the lead in the next phase of global economic development.
The tallest building in the world is now in Dubai, the biggest factory in the world is in China, the largest oil refinery is in India, the largest investment fund in the world is in Abu Dhabi, the largest Ferris wheel in the world is in Singapore.
Whenever societies do well, they believe that there is something in their cultural DNA that made it happen.