These results suggest that Europe became free, and European civilisation therefore became great, due to the ethnic homogeneity of its peoples. Diversity is the Destroyer. Racial purity is the key to freedom and historical success.
As reported in Table 14, column 1 establishes based on data from 145 countries that, unconditionally, the level of predicted genetic diversity within a country in the modern era has a highly significant negative effect on the level of autocracy. The estimated effect indicates that a 1 percentage point increase in predicted genetic diversity generates an 8.7 percent increase in the average level of the autocracy measure over the period 1994–2013.
... Thus, the second layer of the empirical analysis of the determinants of contemporary institutions suggests that the spatial distribution of population diversity across the globe has also contributed to contemporary variation in the degree of autocracy across countries. This reduced-form effect of population diversity on the prevalence of contemporary autocratic institutions across nations may reflect either persistence of institutions from the pre-colonial to the modern era, as established in the first layer of the analysis, or a direct effect of population diversity on contemporary autocratic institutions, capturing the effect of diversity on the demand for institutions as well as for the scope for domination.
...Table 6 establishes that the estimated effect of predicted population diversity on precolonial social stratification and slavery is highly statistically and economically significant, accounting for a wide range of potentially confounding geographical characteristics and continental fixed effects. In particular, a 1 percentage point increase in predicted population diversity increases the score on the social stratification index by 0.1 and the intensity of slavery index by 0.08Source
Ross Douthat, the supposedly conservative commentator in the New York Times, tried to process these results in a way compatible with the (((liberal))) worldview. Rather than reach the obvious conclusion that diversity isn't good and we should seek to avoid it, he instead yearns for a mythical "good emperor" who can somehow make it work.
...From that alienation and fear came Trump, who is barely even trying to reach out and reassure, to make his nationalism seem larger than just white identity politics, to make the groups who feel afraid of his administration sense that he has their anxieties in mind.
There might be a form of nationalism that helps bind a diverse society together, but Trump’s seems more likely to bind a “real American” ex-majority in opposition to every other race and faith and group. His eventual successor, liberal or conservative, should not seek to learn from Assad or Erdogan or Putin. But he (or she) might learn something from an earlier age’s custodians of diverse, fragmented societies — from monarchies like that of the Austrian Hapsburgs, in particular, that worked to contain and balance religious and ethnic divisions, to prevent disintegration and forestall totalitarianism, and might have succeeded longer absent the folly of 1914.
If we’re going to have an imperial presidency, we should want a president who thinks less like a party leader and more like a good emperor — who doesn’t just divide and conquer, but who tries to make all his empire’s many peoples feel like they’re safe and recognized and home.Source
He talks about how the Hapsburg empire "might have succeeded longer absent the folly of 1914" as if WW1 was something that just randomly happened. In fact, it was from the enforced diversity of the Hapsburg empire that the First World War emerged; and the Second World War in turn emerged from the smouldering ruins of the First.
The two most intense ethnonationalist visions of the 20th century, those of Adolf Hitler and Theodor Herzl, were also shaped by the experience of Habsburg diversity. Both men, whose legacies are still with us, concluded that diversity did not and could not work: that the tensions between distinct ethnic groups made disharmony inevitable and effective government impossible. The only way a country could be at peace with itself was when its population consisted of people who empathised with one another because they were ethnic kin.
The peril of diversity is the lesson that should have been learned from the catastrophes of the World Wars. Instead, our rulers have contrived to learn exactly the opposite lesson. History will therefore have to teach it to us again.