To what extent does each state run its own economy? The EU does not have centralised taxes or a centralised economic policy, but it does have a single currency. It's possible a single currency also requires more centralised financial/economic policies.
State economies do differ dramatically though, and monetary policy can indeed affect them in opposite ways at least for a while. And state revenues are almost entirely collected by the state aren't they? There are funds for interstates and railroads, and schools, but often schools are primarily funded at the city level by property taxes.
>The major difference between states is tax rates.
Also tax spending. For example there's no central EU funded military but each member budgets it differently, just like how there's no New York military and Pennsylvania military.
