At the global level, exchange-rate devaluation must be a zero-sum game, with the depreciation of the yen and the euro balanced by appreciation of the US dollar, which is up by more than 15% on a trade-weighted basis since May 2014. Buoyant domestic demand might offset the deflationary impact on the US economy, but only if interest rates stay low enough to stimulate a resurgence of private credit growth, potentially taking us full circle, to the kind of run-up in leverage that preceded the 2008 crisis.