French political economist Thomas Piketty's last book, "Capital in the 21st Century," wasn't just a publishing phenomenon: It drew the world's attention to the problem of growing inequality. In his latest work, the 1,200-page-long "Capital and Ideology," he proposes a solution — in a word, expropriation.

If the first work was largely an economic treatise, the second (so far only available in French) is essentially a political one. It tracks how different political ideologies have justified and promoted inequality since the Middle Ages. To Piketty, the years between 1950 and 1980 were the most successful for "egalitarian coalitions," by which he means parties of the left, but these have since faltered. To address that failure, he attempts to set out a manifesto for the modern left.

To Piketty, 1980 marked a regrettable turning point as leaders such as U.S. President Ronald Reagan and British Prime Minister Margaret Thatcher turned their backs on progressive taxation. He writes: