A full moon rises over New York City as seen from West Orange, N.J., in 2015. Globalization has transformed New York into one of the world’s international hubs. (AP)
Ian Klaus was senior adviser for global cities at the U.S. Department of State and is the author of "Forging Capitalism: Swindlers, Frauds, and the Rise of Modern Finance."

Here’s a proposal for the International Olympic Committee: Next time a country is banned from the Olympics, let its clean athletes compete as representatives of their home cities. The ancient Olympics, after all, were contests between city-states, and with increasing frequency, mayors speak for their residents on the global stage.

Of course, mayors and urbanists still focus on the public square, the block and the sidewalk. At the World Urban Forum  in Kuala Lumpur this week — the year’s biggest urban gathering — bike-shares, automation and housing had their fair share of the agenda.

But cities have become global actors. So the agenda also included climate change, terrorism, populism and equitable economic growth. Mayors are now working across municipal, and even national, borders to solve some of the most pressing global challenges. This would have been unimaginable in decades past: Forty years ago New York was almost bankrupt; 25 years ago Los Angeles was on fire; and less than two decades ago, London did not have an empowered mayor — how did everything change?

Demographics have played a role. A century ago, roughly 10 percent of the world’s population lived in cities. Now, at a minimum, more than 50 percent of the world’s population is urbanized, a number that is expected to grow to more than 60 percent by 2030.

But numbers are only part of the explanation. They don’t translate automatically into efficacy, organization and collective power. Rather, structural shifts in the global economy, changes in the nature of international challenges and improved intercity organizational techniques have all combined to elevate cities on the global stage. In other words, the global city today owes much to the landscape — for better and worse — of U.S.-led globalization.

First and foremost, financial and technological innovations have turned some cities into hubs of the global economy. Since the early 1970s, finance has increased as a percentage of global economic activity, and national governments have focused on maintaining openness, competition and the movement of capital, goods and services.

This new era of economic globalization had profound implications for cities. It favored geographic spaces dense with legal, commercial, financial and even cultural expertise. It also hit traditional manufacturing bases hard. Manchester and Buffalo suffered, while New York, Shanghai and Tokyo became international hubs. And, of course, the revolution in information and communications technology fueled by the Internet has transformed some cities, such as Austin, and more recently Pittsburgh, and other regions into centers of innovation and entrepreneurship.

As the benefits of globalization materialized in select cities, so, too, did the challenges. Consider terrorism. Urban terrorist attacks more than doubled between 1993 and 2000. The city, as Saskia Sassen put it, became what the airplane had been in the 1980s: the target of choice for accessibility, numbers and propaganda. Or consider migration. More than half of the world’s refugees now live in urban areas.

These challenges confronting cities at the onset of the 21st century demanded collective action. One city alone, or a few cities working together, simply couldn’t tackle problems global in scope such as climate change or terrorism.

So, facilitated by the increased ease of communication and often supported by leading philanthropies, cities began building robust networks. London organized C40 Cities (with whom I serve as a policy adviser) in 2005, beginning with 18 cities. Today its network includes more than 90 cities, representing roughly 25 percent of global GDP and more than 10 percent of global population. The Global Covenant of Mayors, meanwhile, connects more than 7,000 cities and towns, including some small towns with fewer than 2,000 residents. There are now more than 200 active city networks, with half cutting across national borders and nearly as many leading to direct policy action.

And while cities often work around the dominant power structures of the nation-state, they have also been working within the traditional international institutions of the post-World War II world — such as the United Nations — to heighten their influence and profile. Some city networks such as United Cities and Local Governments have spent decades lobbying international organizations on behalf of cities. As a result, these institutions have become increasingly accommodating of urban expertise and perspective, which is reflected by international agreements such as Agenda 2030, and efforts to further data collection and research at the city level.

But perhaps nothing has propelled cities’ importance quite like the events of 2016.

Previously, cities acting on the global stage generally sought to further policy goals that paralleled those of their capitals. In 2015, scores of mayors showed up at the Paris climate negotiations not to oppose national leaders, but to support their collaborative effort to tackle climate change.

The Brexit referendum and U.S. presidential election, however, transformed many mayors into the elected opposition. Openness, tolerance and liberalism still have global advocates: They simply sit in city halls, not national capitals. In the wake of the Brexit vote, Mayor Sadiq Khan affirmed London’s commitment to being a cosmopolitan city by advocating that his city devise its own visa system for foreigners. New York City has developed its own ID system, which, among other things, will provide immigrants and others excluded from the formal financial system access to banking.

And the networks and global organizations uniting cities have enabled collective action. In the wake of the White House’s announcement that the United States would leave the Paris agreement, more than 360 mayors assumed a central role in the “We Are Still In” campaign, which works to fulfill the agreement. These mayors are playing on multiple levels, serving their residents at home, while advocating, collectively, on the global stage.

The period of globalization that allowed for and even encouraged the rise of cities may be passing. Great power politics is on the rise again, some of which will be zero sum in nature. But the organizational base for city action has been laid, and the prominence of cities is unlikely to retreat. More likely, the successful great powers will build upon a long history of nation-states and empires working through urban engines and learn to work through their cities, as China already is. We’ve entered into the urban era, and a nation that ignores this fact does so not only at the expense of the global commons, but also at risk to its own interests.