You didn't say how long you have before the debate, but if you have the time read
The Sleepwalkers: How Europe Went to War in 1914
Published in the year of the centennial of the outbreak of the war, it does an excellent job of using all the latest research on causes of the Great War, including whose fault it was and who started it.
Spoilers: no, it wasn't the German Empire. Nor the Austrian, Russians, British, French or even Serbs. Hence the title.
The Sleepwalkers: How Europe Went to War in 1914 is historian
Christopher Clark’s riveting account of the explosive beginnings of
World War I.
Drawing on new scholarship, Clark offers a fresh look at World War I,
focusing not on the battles and atrocities of the war itself, but on
the complex events and relationships that led a group of well-meaning
leaders into brutal conflict.
Clark traces the paths to war in a minute-by-minute, action-packed
narrative that cuts between the key decision centers in Vienna,
Berlin, St. Petersburg, Paris, London, and Belgrade, and examines the
decades of history that informed the events of 1914 and details the
mutual misunderstandings and unintended signals that drove the crisis
forward in a few short weeks.
Meticulously researched and masterfully written, Christopher Clark’s
The Sleepwalkers is a dramatic and authoritative chronicle of Europe’s
descent into a war that tore the world apart.
The best I can come up with is Rube Goldberg... one giant chain reaction of interacting politics, alliances, someone-forgot-to-hit-the-stop-button-in-time.