Economic inequality has become one of the most important themes in the social sciences. The debate has revolved around two basic models. Was Kuznets correct in his prediction that inequality declines with economic growth, or was Piketty, along with others in the Berkeley/Paris/Oxford group, correct to counter that capitalism without severe constraints inevitably leads to increasing inequality? The resolution will depend on long-term historical analysis. In Global Inequality , Milanovic proposed new models to analyze the social, economic, political, and historical factors that influence changes in inequality over time and space. In Capitalism, Alone , he changes direction to examine what patterns of capitalism and inequality will look like in the twenty-first century and beyond, as well as how inequality might be reduced without violence.

The first professional societies in the United States, from the 1880s to the 1910s, understood history to be closely associated with the other social sciences. Even in the mid-twentieth century, history was still grouped with the other social sciences, along with economics, sociology, political science, and anthropology. But in the past few decades, history and anthropology in the United States (though not necessarily in other countries) have moved away from the social sciences to ally themselves with the humanities—paradoxically, just when the other social sciences are becoming more committed to historical research.

Scholars from multiple disciplines generally agree about new models for the origin and dating of migration to the Western Hemisphere, replacing the rigid Clovis-first model that had dominated texts for the past fifty years. This new research has not resolved all of the questions relating to this migration; serious controversies still exist. But the development of the new field of genetic studies and the recent opening of major South American archaeological sites has resolved many older debates and has provided a far more nuanced and complex early history of mankind in the Western Hemisphere than existed before.