I had not known of this important piece. From 2012, by Robert D. Woodberry, at the National University of Singapore:
This article demonstrates historically and statistically that conversionary Protestants (CPs) heavily inﬂuenced the rise and spread of stable democracy around the world. It argues that CPs were a crucial catalyst initiating the development and spread of religious liberty, mass education, mass printing, newspapers, voluntary organizations, and colonial reforms, thereby creating the conditions that made stable democracy more likely. Statistically, the historic prevalence of Protestant missionaries explains about half the variation in democracy in Africa, Asia, Latin America and Oceania and removes the impact of most variables that dominate current statistical research about democracy. The association between Protestant missions and democracy is consistent in different continents and subsamples, and it is robust to more than 50 controls and to instrumental variable analyses.
For the pointer I thank Ann Swidler.