I first heard of Thomas Piketty years ago, and was vaguely aware of him as a radical, but not being an economist I had no detailed knowledge. Now, courtesy of Brighton University running a project on 'Reimagining the Welfare(being) State', I am rather more acquainted with him.
Both the similarity between Piketty and Michael Sandel (both worry about rising inequality), and their differences, show up a long-running argument in moral philosophy (or 'ethics' if you prefer another name). Piketty believes in universal values and principles - seemingly he has to, given what he says about global inequality, tax for redistribution, or neocolonialism - but Sandel believes particular and local concerns have to take pride of place, not least for democracies. Both these thinkers are committed democrats. The argument became charged up over 50 years ago with publication of John Rawls' A Theory of Justice in 1971, but it goes way further back.
In the interconnected world of today (especially apparent when we are fighting) it seems impossible to avoid universals, but psychologically we still want our particular attachments. Personally, I had already begun thinking in terms of some sort of global federalism when I found Piketty himself suggests this, although only related to socialism, itself a very vague concept. I myself would say moral and political federalism, because it is futile to try to separate morals and politics.
An illustration relevant to Piketty's concerns (and to Sandel's and mine) might be to set 'federal' limits to inequality for purposes of preventing unacceptable power concentrations - and avoiding Epstein style abuses. But within those limits localities or particular groups could be left to make their own taxation arrangements.