I have been reading and have some ideas, but apparently even historians are still arguing this one...
Anyway, by 1900 we were fully out of the Dark Ages with the Renaissance & Reformation, the scientific method, the germ theory of disease, the Industrial Revolution, and the Age of Reason. Physics knew everything about space, time and matter with just "a few loose ends" to tie up (hello, Albert!)
...and then suddenly, the most deadly century in the history of humankind. I read 17 million killed WWI, 28 million WWII, and still no end even now 2017.
What happened, why did the assassination 1914 of the Archduke tsunami into WWI?