Their vitality
One reason why the Marshall plan worked was that the Europeans still remembered how to do business within the market laws. There had been only less than a decade between the nazism influence and it's collapse. The people had not forgotten how to make deals.
It's different with the former communist countries such as Russia (70 years of communism=3 generations).
And if Germany and Japan were so great economically, after WW2, it's because they had their whole country to rebuild, from the ashes of war. It made people work and they could build new towns using more recent techniques.
Raoul