The easiest (and hardest) solution ever - fucking ban "offshores". So for example a UN session convenes and passes an extremely simple resolution - all members

The easiest (and hardest) solution ever - fucking ban "offshores". So for example a UN session convenes and passes an extremely simple resolution - all members are instituting a minimum tax (say 15%, for example) for literally everyone and everything. And all countries non-complying must be completely sanctioned a-la Iran. This would take less space than a A4 page and super easy to draft. But of course absolutely impossible to ever pass, just a fantasy. While this is counter-intuitive, since we are talking about taxing billionaires and megacorps etc. to the tune of >90%, but it would actually make those people and companies part with their gains, unlike 90% tax which will never work. Every single company in the world above certain size and every single millionaire and above, are employing criminal schemes to evade paying taxes, declare funds and participate in the economy in other ways. By enforcing a certain minimal tax and banning all "drains" the amount of accrued money would be astronomical. There would be no need for 90%, instead the crazy 50-60% taxes paid by the fools (actual middle class) could be meaningfully reduced to the levels half a century ago and there would still be money left.