Or, you know, we could just seize the assets because of tax evasion. But that will never happen because our politicians are in the pocket of the robber barons.
Many countries have very low (or zero) tax rates, so you can legally set up a company and put your money there.
I think one way to get rid of tax havens is with an international treaty to set some minimum tax rates, and have an embargo against any country that doesn't meet those requirements. It's not just the rich who are to blame, it's the countries that turn themselves into tax havens and make this all possible.