Did they really believe that international warfare would cease, or was it something along the lines of the war being so terrible nobody will want to fight another?
The Great War, as it was referred to at the time was for a lot of people the logical outcome of the stressful times in which they lived. The Austro-Hungarian empire had a lot of internal struggles, as well as the Ottoman empire that was reshaping underneath the pressure of the Young Turks. The German Empire had formed in 1871, at the cost of France having been humiliated and being stripped of the valuable Alsace-Lorraine region (coal). The Serbs were being repressed by the Austro-Hungarians, in which process the former made allies with the Russian Czar. Ever since the two previous Balkan Wars (1912-'13 / '13) it had been a hotchpotch of struggles and Serbia being quite a strategic location it was in high demand to be divided among other bidders.
A general theory in World War I theory by Hew Strachan (2003) states that spirits were high for settlement of the strain that had been looming between the population of different states. In retrospect it has been asserted that people didn't actually take the streets shouting that finally the war had begun, which seems more logical as well. On the other hand though, people did massively volunteer for defending the 'motherland,' even boys beneath the legal age of service.
The item that comes back as well in the Second World war is the threat of Prussian militarism. This is a central theme all were concerned about. Since the unification Germany became one of the predominant powers and so was a grave threat to international stability. In 1947 Law no. 46 was signed, by the Allied Control Council, which stated that >"The Prussian State, which from early days had been the bearer of militarism and reaction in Germany, has de factor ceased to exist." This idea of Germany being a major stem of the evil and outward expansion has its roots in the nineteenth century Imperialism. The German militarism should be met with force, when necessary, or so they thought.
From the off start of the Great War, little people would have predicted such an onslaught. When you look at the soldiers in their coloured country patterns on their horses, swords in their sheaths they thought the war was going to be an honorable battle. The same way in which they sang christmas songs together (Germans and Frenchies) over christmas 1914.
The war was supposed to settle disputes between countries and to even out the distributed power (which we refer to as the concert of Europe). The idea of the post-napoleontic era was that not too much power should rest in the hands of single states. The power balance had to be restored and people just could not have predicted what would happen if so many countries went to war with oneanother with that many technological breakthroughs.