The First World War, that is.
The Telegraph reports that Germany has made the final payment on its reparation obligations for World War I. (Actually, it appears that the payments being made by Germany since the end of WWII were not technically the reparations themselves, but rather repayment of bonds that were issued under Weimar to help fund the reparations. See this link.)
A Cato writer says: As Keynes rightly predicted, the unreasonably high French demands for financial reparations led to German economic weakness. The end result was hyperinflation, which was one of the principal causes of Hitler’s rise to power and the start of the Second World War. In spite of losing two world wars, Germany did eventually become the most powerful nation in Europe — through trade, capitalism and German ingenuity.
Actually, the hyperinflation was by no means the inevitable result of the reparations payment—these would have been burdensome and painful to Germany regardless of how the economy was managed, but it was the severe mismanagement of economic policy that caused hyperinflation to result. See my post an architect of hyperinflation.
Germans deserve great credit for their remarkable economic performance in recent decades, but, as Glenn Reynolds notes–and the Cato article did not–the U.S. military umbrella played an important part in enabling this to happen. The Marshall Plan was also a significant factor in the postwar recovery.
The social and political effects of the Great War are, of course, still very much with us.