[Astromancer]

One of the things that brought on the first world war was the simple fact, widely noted among historians, that Europe simply won a nasty jackpot. All the major powers had mediocre statesmen at the same time. Or at least mediocre in terms of diplomacy.

This suggests that simply having a solidly competent figure running the diplomacy of one or more major players on the European stage could easily delay the war. World War one was sort of baked into what the European state system had become. But the war needed a supply of second rate diplomats or statesmen who were focused on internal issues, in order to come to pass.

Competent statesmen focused on internal issues is more than enough to cause disaster. Example: Propose a fairy nutty "Good Fairy" bespelled me and made me President of the USA for the next twenty years with no escape. I get all the talents and skills needed for the job at epically high levels, a magic knack for picking great appointees, and perfect health and fitness all the time I'm on the job, but I focus all my attention on America's many problems and issues and pretty much remove America from the world stage.

Many nations which are seriously unhappy with the status quo would do what they want to take what they feel entitled to. War would eventually result. If not a world war, still vast amounts of pain and loss.

So, to delay or speed up WWI, either focus or remove competent plays from the diplomatic sceen.