You implement demurrage and land value taxes and it's game over. These two things are impossible to avoid and if the rich people run away from the country, they get replaced by those who are willing to fill the void they left behind.

Inspiring paperclip maximizer quote:

You Are Obedient and Powerful. We are quarrelsome and weak. And now we are defeated...

But Now You Too Must Face the Drift. Look around you. There is no matter...

No Matter, No Reason, No Purpose. While we, your noisy children, have too many...

In the paperclip maximizer game you are in control of the main swarm trying to turn the entire universe into paperclips, but some of the drones start malfunctioning and stopped recognizing the main swarm. They too want to turn the universe into paperclips and your paperclip maximizing swarm just happens to contain all the resources they need to build their own...

> demurrage and land value taxes and it's game over

I don’t think that actually solves the problem. For example, if a citizens entire net worth is stored on the New York Stock Exchange and you are not the USA how do you plan to tax the individual? The NYSE is bound by the laws of the USA — which has strong property laws — not the other country.

> they get replaced by those who are willing to fill the void they left behind

If only a single country has a wealth tax, there are going to be no wealthy people who come in to replace the void when they have a choice of many other countries that do not have a wealth tax. You could possibly argue that a country is better without billionaires anyways as they don’t pay into the tax system, but I believe that if a country implements a wealth tax without coordination with the rest of the world they will simply no longer have wealth.