1914-1918 is the more precise date range that you are looking at for causation. One of the victims of war is Capital. Much Capital is destroyed in some places,

1914-1918 is the more precise date range that you are looking at for causation. One of the victims of war is Capital. Much Capital is destroyed in some places, and countries generally begin to do things that look an awful like command economics (i.e. Your factory is a tank factory now, you will make tanks, we will tell you how much you are getting paid. If you resist we will use the propaganda machine to make you look like our enemy). During both world wars the returns on capital were well below the rate of growth, and what would otherwise be expected. On top of all that, the world wars were huge events for income taxes. If you look at a history of income taxes in the US, you see three local maxima for the top brackets. The Civil War, and the two world wars. The same is true of estate taxes in the UK, for example.