Wealth is not fixed and is entirely the result of human work and ingenuity. In 1945 Japan was bombed flat, and there was starvation. All of the heavy industry in the country had been targeted and completely destroyed the by Allies. They also just had a huge, productive piece of their population disappear. Japan has only one natural resource, and that's it's people. The USA gave them some money but the Japanese people did the work and the nation was an economic powerhouse again in twenty years, within thirty they were outcompeting everybody. Now they are fabulously wealthy with the most technologically advanced country in the World without oil wells, or coal mines, or mineral deposits, or sustantial farmland, or forests they will cut down.

Oh, the Japanese were also a horrible colonial power like the USA and the UK, and also best pals with the Nazis. The Koreans and the Chinese still hate them. If WW II wasn't a "Dark Age", I don't know what was.