Chapter 10 presents case study evidence for the foregoing theory from colonial areas under the control of a single European colonizer. It focuses on four European empires – British, French, Spanish, and Portuguese – because of their extensive historical literatures and because they have the greatest within-empire variation. These cases demonstrate that Europeans brought representative democratic practices (along with their religion, culture, language, and technology) to their colonies and that they spread these institutions where they (Europeans) were sufficiently numerous to control the political outcomes. As a result, democracy became a tool of white supremacy.

Chapter 11 presents statistical tests of the relationship between European ancestry and democracy. A wide range of model specifications is utilized including varying measures of democracy, varying measures and temporal configurations of "Europe," and varying samples. The chapter also replicates previous work in this area and demonstrates how the theory serves to complement extant research. The chapter concludes with some estimates of the causal impact and a discussion of challenges to causal inference in this context.

Where previous chapters offered robust evidence of a correlation between natural harbors and democracy, Chapter 7 explores a possible causal relationship between these factors. Several plausible causal pathways are considered: economic development, state size, social diversity, and democratic values. The chapter concludes with a formal mediation analysis of these possible causal mechanisms, finding that there is support for economic development, state size (though attenuated over time), ethnic diversity, and democratic values.

Chapter 6 presents statistical tests of the relationship between natural harbors and democracy. Tests of the early modern era utilize a limited dataset from the Ethnographic Atlas while later tests offer broader coverage using a variety of regime type indicators. A wide range of model specifications are utilized including varying measures of harbors and harbor distance, varying measures of democracy, and varying samples. The evidence that natural harbors have a positive correlation with democratic regimes is robust to all of these different model specifications. The chapter concludes by considering the waning of this effect over time.

Chapter 13 explores alternative theories of how democracy spread from Europe to other regions of the world. Specifically, we look at theories related to colonialism, religion, and language. The chapter provides empirical tests of each of these theories and attempts to compare the relative importance of each. The tests suggest that each of these pathways is plausible when tested in isolation but that European ancestry is the strongest predictor. We also note that the effect of Europe on democracy varies through time, with a peak during the early twentieth century and an attenuation since then.