You can have private cities competing with each other for people to live there. Of course some kind of 'government' is also necessary in a private world with no nation states; it makes a huge difference how states and companies operate. A corporation without the ability to lobby a state has to fulfill customer's wishes in order to succeed; the state has the monopoly on force. Many small competing private cities besides small governmental entities like Liechtenstein would be great for humanity as you could easily escape if you don't like it.

You sign a contract with a private city where the terms and conditions are defined and cannot ambigously be changed - a real social contract so to speak. There are many different models for this, Murray Newton Rothbard and Hans Hermann Hoppe have theorised about total private social orders. Titus Gebel wrote a book about the private city model and he is trying to make this a reality - I highly recommend reading this book as it provides a very practical view.

You can also stick to the classical liberal side as Ludwig Edler von Mises did; a state needs minimal 'income' in order to fulfill the basics. This can be financed via a flat general added tax on goods and serviced and nothing else, keeping things simple. This would make gigantic bureaucracies like the IRS and the military-industrial complex obsolete and all the people working for them. These people would work in areas being more productive for humanity.

In general, a mixture of private models with smaller, decentralised states would be doable for humans. More competition, more ways to escape fiscal tyranny are for sure contributing to peace and prosperity in the long term. The founding fathers would be ashamed to see what a gigantic Leviathan the US government has become.