This chapter explores how the major powers of Europe and the USA mobilized their economies when war came in 1939, and how at the end of the Second World War they once again wrestled with the problem of how to restore economic peace. Viewed in terms of strictly economic metrics it is conventional to draw a sharp line in 1945 separating the troubled interwar era from the 'post-war' era of triumphant growth. In terms of economic success the difference is undeniable. But the moniker of 'post-war' is seriously misleading when applied to the 1950s, a period of intense military confrontation in the early Cold War and violent decolonization struggles. Alongside the famous welfare state initiatives of the 1940s, the warfare states that had first taken shape in the First World War were more entrenched than ever. Recognizing this casts new light on the nature of the 'post-war' international economic order.