Currency wars are necessary if all else failsThe atomic bomb, of course, is quantitative easing by the Federal Reserve. America has in effect issued an ultimatum to China and G20: either you stop this predatory behaviour and agree to some formula for global rebalancing, or we will deploy QE2 `a l’outrance’ to flood your economies with excess liquidity. We will cause you to overheat and drive up your wage costs. We will impose a de facto currency revaluation by more brutal and disruptive means, and there is little you can do to stop it. Pick your poison.