 Daron Acemoglu and James A. Robinson used the economic histories of Sweden and South Africa to show that social inequality depends much more on institutional factors than Piketty's factors like the difference between rate of return and growth.Cross-country analysis also shows that the top 1%'s share of income does not depend on that difference.The professors write that general laws, which is how they characterize Piketty's postulations, "are unhelpful as a guide to understand the past or predict the future because they ignore the central role of political and economic institutions in shaping the evolution of technology and the distribution of resources in a society".