I'm not too sure on the first one since those two brothers could easily age well thanks to their powers/background.
In retrospect it makes sense to see so many world wars since unlike us they have no large scale deterrents like say a Rinnegan factory. If every nation had something like that or Edo Tensei users bringing out disposable Kage level ninjas to carpetbomb cities they would be even less enthusiastic about war than they already are. Winston Churchill tried to START WW3 barely a week after WWII was finished.If it wasn't for the possibility of nuclear escalation we'd have probably had more world wars than two by now.
XI Wiki


