I imagine if you had the right conditions between Austria and Serbia...Austria controlling Serbian national provinces, for example...you could have an "Assassination of Archduke Francis Ferdinand" event, and let it go from there. If Russia is guarenteeing the independence of Serbia, it will go to war with Austria.
With the right alliances in order, you could have something resembling WWI, but you shouldn't have an event to bring each combatant in.
Of course, there could be events to set these alliances up, such as the Three Emperor's League (with an event to have Russia leave it), the Franco-Russian entente, Italy's defensive alliance with Austria/Germany (Italy shouldn't get involved therefore is Austria is the aggressor). I'm not sure about Britain, though. The treaty it used to go to war with Germany was the Treaty of London, signed in 1836! I'm not sure Britain will still be guarenteeing the independence of Belgium by then, but perhaps if conditions are right (Britain signed the treaty early on, has friendly relations with Belgium and France, and no alliance with Germany), an event could be worked to bring Britain into the fold.