From an economic point of view World War II was, above all, a burst of deficit-financed government spending, on a scale that would never have been approved otherwise. Over the course of the war the federal government borrowed an amount equal to roughly twice the value of G.D.P. in 1940 — the equivalent of roughly $30 trillion today.
Had anyone proposed spending even a fraction that much before the war, people would have said the same things they’re saying today. They would have warned about crushing debt and runaway inflation. They would also have said, rightly, that the Depression was in large part caused by excess debt — and then have declared that it was impossible to fix this problem by issuing even more debt.
But guess what? Deficit spending created an economic boom — and the boom laid the foundation for long-run prosperity. Overall debt in the economy — public plus private — actually fell as a percentage of G.D.P., thanks to economic growth and, yes, some inflation, which reduced the real value of outstanding debts. And after the war, thanks to the improved financial position of the private sector, the economy was able to thrive without continuing deficits.