Austria-Hungary and Germany saw an opportunity to conquer and took it

The assassination of Archduke Franz Ferdinand should not be written off as an unfortunate incident with disproportionate consequences inciting an entire world war. It was clear that the drift growing between European powers led the duo of Austria-Hungary and Germany to go on the offensive, using the assassination as a guise. The balance of power in the European theater was veering away from Austria and Germany, resulting in them entering a state of policy where they would need to restate their own dominance in an effort of self-preservation. Specifically, the Austrians were already threatened by Serbian ambition in the Balkans and had felt a need to secure themselves in that sphere. The assassination resulted in an increased threat of military invasion, backing Austria and Germany further into their corner of the continent.^[1]