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Inequality has been rising in most countries around the world, but it has played out in different ways across countries and regions. The United States, it is increasingly recognized, has the sad distinction of being the most unequal advanced country, though the income gap has also widened to a lesser extent, in Britain, Japan, Canada and Germany. Of course, the situation is even worse in Russia, and some developing countries in Latin America and Africa. But this is a club of which we should not be proud to be a member. Some big countries — Brazil, Indonesia and Argentina — have become more equal in recent years, and other countries, like Spain, were on that trajectory until the economic crisis of 2007-8. Singapore has had the distinction of having prioritized social and...