In the ancient world, there were once city-states. These were cities that were also states. But today, a city is seldom a state in its own right. Cities do not retain sovereignty over themselves. They are mere municipalities, subject to the rule of other, bigger entities called countries, or nations, republics or monarchies.
What are some famous city-states from the past? Tyre and Sidon come to mind. Also Babylon and Ur. Athens and Sparta were successful city-states, as was Rome, before it came to be a major world power. But now, look around the globe, and how many city states can you think of?
There are only a handful:
What if every city were a city-state? Would this be a world full of chaos and war, or might it not be a more peaceful world, because every city could make its own laws, laws that are pleasing to its own citizens. And if you do not like the laws? Then move to another city!