I would suggest you read up on the history of mercenaries worldwide and the history of youth volunteering for wars worldwide. These are by no means traits particular to Japanese people. I would also suggest you read up on the United States global positioning before and after WW2. It was regionally isolated from the brunt of the war, which allowed it to loan money and sell weapons and resources at very favorable rates for the majority of the war. This can’t be excluded from a simple explanation of its global dominance.