Does your world have a world war scenario? If so, how does it play out?

For example, Laniakea has a world war called the 'Great War' or 'The Purge of Nyan', when the Fascist Nyanese Mandate declared war by attempting to assassinate Queen Asra Drakensar of the Celestial Empire.

Simultaneously the Keyitian Divine Mandate (japanese empire type country) decared war on Kisto.

This turned into a war between the NSA and the Allies (NITO and the Celestial Empire.

(It's better when explained not so briefly, but y'know, time and all that. Wot wot.)