Why German was so strong? I think after WW1 the other countries were weakened and they didn't want to fight anymore
While most of the German people kinda wanted a revenge, and it eventually burst
I think it is more relevant to personality of a country
Germans have very solid spirit and they won't betray each other.
Also they love their own country, so they devoted all their power.
For Japan, it is similar.
And Chinese could not group together and betrayed each other at that time, that's why China was so weak.
Up till now both Japan and Germany are still strong countries.