I disagree. The alliances are fine even if you don't manage it usually they just stop, however that is not the same as war.

The reality is simpler, there was a group of people in Austria who wanted war with Serbia, and a group of people in Germany who wanted war with Franz and Russia. Unfortunately for world history those people happen to be in particular places at that time, and so they started the war.

It is really that simple, a number of people wanted war, so they started it.