World War I was the war that should not have happened.
Once it did World War II was pre-determined by how World War I ended and made a necessity.
World War I the root of all evils from Communism to Naziism and all we have seen since including the recent events related to Ukraine.
There are good arguments that WWI was inevitable.
Germany had gone off and made an enemy of Britain, for no good reason. Germany likewise had abandoned its Russian alliance. And the overall extremely rapid rate of technological and economic development permitted most nations to raise and maintain vast armies. All itching to be used.