What makes democracy happen?

Social scientists in Europe and the United States collaborated on an immense study, using a statistical technique called "extreme bounds analysis" to assess which of 59 different factors and conditions seem to support or inhibit the development of democracy through history and around the world. In the end, they found few, and the ones they considered reliable have a high "well, duh" factor. They concluded:

We conclude that while there are many plausible theories of democracy, there are few robust predictors that we can trust as reliable. For policymakers interested in promoting democracy based on such reliable predictors, we suggest that there is little difference policy can make when it comes to the emergence of democracy.

History, in other words, is not so predictable. Who knew? (Historians.)