WWII Bombing and the German City System: Back to the Synthetic Mean?

We study the postwar effects of the bombing of German cities during WWII on urban growth and use the synthetic control method (SCM) to construct comparison units for affected West-German cities. The reason for using SCM is that cities might experience structural changes that have nothing to do with the bombing of cities. Ignoring these structural changes could incorrectly attribute the postwar change of cities to the WWII bombing shock, while other factors are at work. The SCM takes these structural changes onboard. Synthetic units are used as counterfactuals to assess the long-term impact following the WWII bombing on the size distribution of 53 West-German cities. Our main contribution is that we do not only study whether bombed cities are mean-reverting, but also use the counterfactual to determine whether individual cities experienced a positive or negative impact. In general, we find mean reversion for 50–70% of the cities, as well as a roughly balanced ratio of positively to negatively impacted cities with a unit root.