This is a false premise, and a dangerously alt-history question. The First World War was very much not inevitable, and such arguments have fallen completely out of credible use in the historiographical academia for quite some time now, beginning with the shift away from the "Big Causes" that are highlighted in this Monday Methods post.

The problem (well, one of many) with arguing that the First World War was "inevitable" is that it completely ignores the importance of contingency throughout the events of June- August 1914. There were opportunities for a more peaceful resolution following the assassination of Archduke Franz Ferdinand, and even Imperial Germany was aware of such outcomes - indeed right up until the end of July the Kaiser and many of his ministers were eager to "localize" the conflict to a "Third Balkan War" of sorts.

Secondly, the major issue with propagating an "inevitable war" thesis is that it immediately nullifies the historiographical need for explanations regarding why the war broke out in 1914 when it did (or more specifically, why an Archduke's assassination led to a continental European conflict). By simply stating that it would have happened anyways, the value of theses and investigation (and there are thousands of them and counting) on the events of the July Crisis is reduced significantly. It is also, as mentioned earlier, egregiously alt-history leaning to suggest that World War I would have happened regardless of whether the Archduke's assassination triggered the diplomatic crisis that it. Whilst there were certainly voices in each of the capitals of Europe arguing for war against a specific enemy (i.e an Austro-Hungarian-Serbian conflict or a Russo-German one), they were a minority in the halls of power.

Thirdly, the thesis that World War I was inevitable feeds nicely into a more established theses which was quite popular in the Cold War era: inadvertent war. Simply put, this thesis argued that none of Europe's leaders knew what they were getting into during the July Crisis, and as such (to quote Llyod George's lovely little misleading phrase), "the nations slithered over the brink into the boiling cauldron of war." As Hamilton and Herwig point out, the reality is quite the opposite:

"Nations do not simply "slither" into wars, driven by overpowering dark forces. Human beings at the highest levels, leaders, elites, decision makers, collect information, evaluate their chances, and make decisions. Their choices may have been mistaken, flawed, and ill-chosen. But their nation's involvement stems from a choice based on some kind of intention...the leaders of the various governments in 1914 assessed their options, weighed the choices, and, fully aware of the most likely consequences, deliberately chose involvement."

To conclude then, it is difficult to point towards a possible event which may have led to a diplomatic crises which Europe experienced in 1914, precisely because of the fact that such a crises guarantees nothing. For all historians are able to predict, if Princip had shot the Archduke a year earlier or a year later, it might have completely changed the history of 1914-1918. As A.J.P Taylor remarks rather aptly:

"No war is inevitable until it breaks out"