If you only look for causes and explantations on a surface level you wont find much and you will be easily mislead.The main event and reason of the war was the violent uprising of the third estate, to crush the last remainders of monarchy aristocracy and order around the world, you might be familiar with terms such as "the war to end all wars" or the crusade of democracy and so on. And if you look at the effects you can clearly see the traces of the hidden forces at work, even more so their devastating results, the hellhole we live in today. Given, WW2 was a last upheaval or more of a immune reaction of the all to quick rise of the fourth estate, but ultimately that too failed.
Also >muh x million people... I dont want to sound insensitive, but there have never been so many people on here and there where never supposed to be that many, arguing in quantity like that is confusing at best, rather one should look at the damage in quality, the drop in level, which even led to far more lives lost.