alt Hacker NewsOne can make an excellent argument that WWI started because Germany's last Kaiser - https://en.wikipedia.org/wiki/Wilhelm_II - was a narcissistic, blundering man-child.
(Not to say that any other nation's leaders were models of wisdom and responsibility.)
Where else might we find narcissistic, man-children elevated to dangerous levels of authority?!? (most likely that was your point)
I saw a fascinating documentary addressing the fact that the 3 primary leaders of the belligerents in WWI were competitive cousins - amazing that Nicky, George and Little Willi all knew one another as children! And yes, the analysis was that Wilhelm felt excluded and was never very mature - sorry I don't remember the documentary title but there is a summary of the facts here: https://www.bbc.co.uk/history/british/britain_wwone/cousins_...