The most important characteristic of the 21st century is the rise of cities. The world may obsess over whether a “Chinese century” is replacing an American one. But the real action is not in nations, but in their urban centres.

For the first time in human history, more people now live in cities than in rural areas. By 2050, 6.5 billion people, two-thirds of all humanity, will live and work in cities. In 1950, fewer than one billion did so.

But not all cities are equal. Global cities — leaders in commerce, arts and education — rise above the rest. They have the scope, ambition and clout to shape not just the world’s economy but also its ideas, culture, policies and future.

Big and connected, they transcend borders and disrupt international agendas. They are magnets for business, people, money and innovation.

Today, when we talk about non-state actors, we tend to think of terrorist groups, such as Al Qaida and Daesh (the self-proclaimed Islamic State of Iraq and the Levant) or global corporations, such as Apple and BP. But it is in cities that the real power beyond the state resides.

Indeed, today’s international politics is beginning to resemble the Hanseatic League of medieval cities, with global centres trading and working together to address common problems in ways that large nations do not. While not sovereign, global cities are increasingly independent — driving policies that stimulate wider change. They drive the world’s economy. The 600 biggest cities account for more than 60 per cent of global gross domestic product. The top 20 are home to one-third of all large corporations and almost half of their combined revenues. Tokyo leads the pack — in population size, economic punch and number of corporate headquarters — ahead of New York, London and Paris.

Cities only cover two per cent of the earth’s surface, but they consume 78 per cent of the its energy and account for 60 per cent of all greenhouse gas emissions. And while nations debate over what to do about climate change, the largest and most important cities are getting together and doing something about it.

One such effort is the C40, a group of 75 major cities that gathers and exchanges data to enable concrete actions to tackle climate change. In thousands of ways, from energy-efficient street lighting to improved public transportation, big cities are making a real difference on global warming.

Cities are also increasingly pursuing their own foreign policies. Shanghai has its own foreign affairs office, while Sao Paulo has established diplomatic relations with dozens of states. These nations, in turn, have larger diplomatic representations there than they have in the capital Brasília.

Major capital cities, such as London, Tokyo and Paris, are integral to the foreign policies of their national governments. But global cities that are not national seats of government, such as Chicago or Shanghai, increasingly need to forge foreign policies of their own by co-ordinating the global engagement of its corporations, top academic centres, cultural institutions and civic bodies in ways that benefit the city and its citizens as a whole. Greater strategic direction, more cooperation and better coordination of such global engagement would constitute the equivalent of a foreign policy for Chicago.

In short, global cities are increasingly driving world affairs — economically, politically, socially and culturally. They are no longer just places to live in. They have emerged as leading actors on the global stage.

— Financial Times

Ivo Daalder is president of the Chicago Council on Global affairs, which together with the Financial Times is hosting the Chicago Forum on Global Cities.