In WWI, the victor Entente nations seemed to go through an economic boom after the war all the way through the Great Depression. Meanwhile, the economic boom after WWII reconstruction seemed to last decades and both the Allied and Axis nations benefited greatly (Baby Boomers, the Japanese Miracle, Wirtschaftswunder); not only just pulling themselves out of the Great Recessions but reshaping global economics/trade. What was different about WWI and WWII that allowed the sustained economic for growth in so many nations for so long?
Thanks
Paul Kennedy has an interesting analysis on this in his book Rise and Fall of the Great Powers.
It has a lot to do with the condition of the nations after the two wars. In each case the US had received a huge boost in production during the war and was driving the boom. But there were several differences.
After WWI the credit markets in the US were relatively immature. New York had displaced London as the financial capital of the world, but it really wasn't ready to do so. They over-extended their lending... and when the market corrected the government reacted in a way that would have been ok for a second tier country, but not a world leader like the US had become. They tightened rules and monetary access. Basically part of the Great Depression was set off because the US was acting like an isolated nation. And the old first tier economies namely Great Britain, but also France and Germany (and Amsterdam to a lesser degree) didn't have enough liquidity to correct for the problem, especially with the US calling in overseas loans.
The second problem after WWI was although the US economy was booming, no one else's had systemic problems. Once the initial war problems were over, everyone else's economies recovered really quickly (except Russia's). Production soared, especially farm production. So there was a glut of both commodity and finished goods which drove prices down to record lows. Excess production and reduced demand is a great mix for deflation and unemployment.
In contrast after WWII the US had several advantages. One was everyone else was annihilated. Unlike 1918, German workers couldn't go home and go to work in the factories. In 1945 all the factories were rubble. The transition from a war economy was a much longer and gradual one. Most of the other powers had to rebuild, and they had to buy from the US to do so. The US was able to convert production capability to meet first reconstruction and then consumer goods needs.
The second was the US had a much more robust and mature finance and banking system. So it was able to continue paying the interest on the loans on the war. It was also able to float massive new loans and grants to encourage everyone to "buy American."
The third was this increased government spending never stopped. Once the war was over, reconstruction began. Once reconstruction was over the Cold War and the Korean War had begun. Then space spending like the Apollo program. With such massive spending consistently stimulating demand, there was always an engine driving the market. That reassured lenders, who made credit available to consumers, who bought houses and other goods, which were made by people who had to hire more workers, so they had to compete to hire those same consumers, driving up wages, which made more money available stimulating more consumption. It was a very virtuous cycle.
This all eventually reached a new equilibrium. But because everyone had to dig out of the mess that was WWII, the equilibrium was reached more gradually. Where as in WWI the "equilibrium" was reached much quicker, and as such it proved only to be a temporary equilibrium.