Goodbye nation-states, hello city-states
Ever bigger cities, seeing themselves as culturally unique and more ideologically nimble than the nation-states they belong to, begin to detach themselves and declare independence. New cities will be founded and managed with specific rules for specific purposes such as commerce, technology incubation, manufacturing development. Others will have nothing to do with economics and everything to do with protecting cultural traditions, all creating a cross between global freedom of choice and gated communities.
Ideally, each city would be open to anyone willing and able to make a contribution and individuals would be able to prosper in a political and cultural setting best suited to their own mindset (under conditions determined by each one). Future independent geopolitical divisions will be based on similarity of ideas rather than ethnicity or place of origin. With atomized regions each mastering their own speciality and individuals free to prosper in a chosen setting, quality of human ideas and product would flourish.
According to a Gallup survey, the populations of Singapore and New Zealand would double if people had the freedom to emigrate anywhere in the world, while other countries' (Zimbabwe, Sierra Leone) would halve and others would alter radically (Switzerland). Sovereign city-states merely reflect the desire of humans to pursue their lives and ambitions in appropriate places, while the current situation demonstrates their lack of freedom to do so.
This is neither a radical nor even original idea, and has been common in various places and at various times throughout history. Ancient Sparta, Athens and Mesopotamia were sovereign, as were medieval Venice and Florence. The city of Lubek, part of the Hanseatic League of the Holy Roman Empire, was independent until the late 19th century and there have been a smattering of geopolitical anomalies ever since, from Tangiers and Jerusalem to West Berlin. Modern-day examples are Singapore, Hong Kong, even Vatican City and Monaco. Regardless of opinions about the governance or cultures of these places, each has been undoubtedly fascinating and has punched above its weight in world attention.
Some argue the world's future is becoming more united, more standardized and homogenous. Technological advances dictate communications will remain open and standards of commerce and interaction will remain between city-states. But just as the internet has opened minds and broadened knowledge of the world's different cultures, it has also compartmentalized and narrowed focus of interest, bringing together people with shared ideas from widespread areas while highlighting differences with people nearby (eg: you have a best friend you've never met in person, but you don't have anything in common with the guy next door). City-states will be a physical manifestation of this phenomenon.
Of course, this future won't always be pretty. Ideological experiments often go wrong. Many city-states, rather than being shining temples to individualism and freedom, will be virtual prisons of their maltreated inhabitants as some nations are today. Some will exploit desperate minorities for the benefit of their elites. Many will seem like dystopias with cultural practices repugnant to outsiders. And while cities are powerful incubators of ideas and commerce, by themselves they are poor providers of food, water, materials and garbage disposal. There will be tension between city representatives and advocates of farmers and other rural dwellers in the surrounding lands, who won't be going anywhere. Conflicts, sometimes violent, will still occur but will be localized and contained, unlike the Total War scenarios of the 20th century.
Eventually the temptation to unite, expand and dominate might see city-states absorbed into new entities resembling today's countries. The drive to link and separate may be part of a larger cycle with cultures alternating between the two. But the world will always decide what it prefers through trial and error, and future city-states promise to bring much of both.