What they're talking about is the creation of the Military Industrial Complex but without directly saying it. New Deal programs were replaced with military ones and American production shifted heavily into a constant state of arms production.

The reason it "helped the economy" had nothing to do with war or violence, just the fact that military production lines require massive amounts of labor and are centrally planned and funded by the state.

If America had decided to centrally plan light industrial production and invest in infrastructure (continuing New Deal policies) it would have had the same effect, but you can't genocide Koreans with trains in Chicago.