This is a little bit debateable... While the first world war was a direct result of firstly Austria-Hungary issuing an ultimatum to Serbia after Archduke Ferdinand was assassinated, and Germany (Austria-Hungary's ally) declaring war on Russia (Austria Hungary's ally) because Serbia and its ally Russia had been getting all threaty, then deciding to sort out France (Russia's ally) via Belgium to bypass the Maginot line, there were many deeper causes... Such as military build up, imperialism etc - basically both sides wanted a scrap to see who had built their war machines better, and propaganda on both sides had built up the others to be monsters ("they eat babies!!!"). Hence a great deal of enthusiasm from yer patriotic folks to go and get slaughtered cos the generals were rubbish!
Then the Treaty of Versailles beat Germany sufficiently to cause resentment, which encouraged the rise of Hitler, but not enough to stop them rebuilding with ease once Adolf got the Daily Mail and Edward VII on board!
or at least that's what we were taught for history O level...