Historians still scratch their heads over the beginnings of WW1. I don’t know why. Europe was effectively packed with explosives and gasoline just waiting for some damn fool to do something stupid. What is going on in Ukraine today is just like that. In 100 years (if anybody is still around) future historians will be wondering at the grand stupidity of it all.
The players leading up to that war are so all over the place. In the end it brought down the Austria-Hungarian and Ottoman empires. It also saw the height of the British empire and the emergence of the US.
It also destroyed a generation of the best and brightest young men Europe and UK had.