Economic historians have jumped on a trend of pinning differences today to events that happened hundreds of years ago. In some cases, the empirics are convincing and there is a theory to explain why it is not just a coincidence. (Coincidences happen!) Two examples: the roots of German anti-Semitism and the effects of the slave trade on Africa.
But sometimes the effect is either trivial to those who know the history (the ejido in Mexico) or simply hard to fathom. One of the latter is a famous finding by Daron Acemoglu (MIT), Davide Cantoni (Ludwig-MaximilliansUniversität), Simon Johnson (MIT) and Jim Robinson (Harvard) on the effects of French expansion during the Napoleonic Wars. Where the French army went in Germany, they find, urbanization increased later. The proposed mechanism are the reforms the French brought. Vive la révolution!
Or perhaps not. In an intriguing paper, Ece Guleryuz shows that urbanization also increased faster in the French departments closer to the Franco-German border. Since all of France underwent French revolutionary reforms, this result cast some doubt on the importance of Napoleon to later German economic growth.
The below map (I think, I dashed it off myself using the definitions in Appendix A) shows the areas under French influence in blue. The provinces that the authors of Acemoglu et. al. used as controls are in brown and red. (They used two different control areas.) The areas under French occupation are unsurprisingly closer to the postwar Franco-German border.
Since the article appeared in the American Economic Review, it has been taken as the canonical case that it is at least possible for foreign armies to impose long-lasting institutional change. But perhaps it is not so certain.