According to research based on The World Top Incomes Database, this decline in inequality began in North America and much of Europe in around the 1920 and 1930s and a little later, perhaps the 1950s, in some developing countries. But then, in the 1970s and 1980s, the pattern began to reverse, and inequality began to rise again. That shape, incidentally, is the inverse of what some economists predicted would happen (see Section 4.1).