You forgot when austria sent Serbia a Impossible to fulfil ultimatum,
#go and make a presentation

Also Russia then the protector of the Slav nations joined, and France was allied with Russia and the Uk and the USA joined and Germany and turkey joined the Central powers and Italy and Japan joined the triple entente since Italy was in a defensive pact called the triple alliance. So Italy stayed neutral until the pact of London
My presentation of World Wars
World War 1 came on June 28, 1914, when a young Serbian patriot shot and killed Archduke Franz Ferdinand, the heir to the Austria, in the city of Sarajevo. The assassin was a supporter of the kingdom of Serbia, and in a month, the Austrian army invaded Serbia. Then more countries started joining the fight, until it was the whole entire world, and instead of a battle between Austria and Serbia, it was more rather a World War than a small battle.