The use of shell companies and tax havens isn't new, but it's an increasingly important subject, and not just because the Panama Papers leaks have it in the news. According to estimates from UC Berkley economist Gabriel Zucman, the share of global wealth being held in these kinds of structures has skyrocketed over the past quarter-century:
Pretty much any tax regime you can think of is going to have some exploitable loopholes. If you don't do anything to change the system, over time those loopholes are going to be found, publicized, exploited, and expanded. Eventually, their use becomes so simple and routinized that whole industries are dedicated to guiding tax avoiders through the process and foreign economies (like the Cayman Islands) are based on protecting the gains.
In a functioning political system, this becomes a cat-and-mouse game where the government closes the loopholes and the lawyers and accountants try to keep discovering news ones. But across much of the world, the cats — inspired by anti-tax ideology — have been deliberately falling further and further behind, and the mice are acting with more impunity. That's what you see on this chart.
The result is a world in which it's hardly fair to call things like tax shelters in Panama "loopholes" anymore. They are a visible, persistent part of the global tax system, and the authorities behind that system have implicitly signaled that it is safe and even acceptable to use them.