Not all of them believed this necessarily. The Germans for instance had a pretty clear picture (relative to everyone else) what a WW1 battlefield could turn into. They did not expect a short war with a decisive battle as much as they felt their only chance of winning was a short war with a decisive battle, and their entire strategic plan was to force this battle by turning the flank of the French, getting behind their lines of defense and marching towards Paris without facing organized opposition in prepared positions. As early as the 1870 Franco Prussian War Helmuth von Moltke, the German Chief of Staff recognized that warfare had changed in a very fundamental way. The Germans had broken the French in battle early and captured the French Emperor but the French were able to replace their losses with astonishing speed by conscripting more men under a provisional government. When Bismarck wanted to negotiate peace terms von Moltke lobbied to continue the war to devastate France to the point they could not come back and fight again, because he feared the depth of a new conflict fought by massive conscript armies. This is a quote by von Moltke on the possible ramifications of a new European war:

"If war should break out no one can estimate its duration or see when it will end. The greatest powers of Europe, which are armed as never before, will fight each other. None can be annihilated so completely in one or two campaigns that it would declare itself vanquished and be compelled to accept hard conditions for peace without any chance, even after a year’s time, to renew the fight. Gentlemen, it might be a seven, or even a thirty years’ war – but woe to him who sets Europe alight and first throws the match into the powder-barrel!"

This fear was essentially baked in on the German side, and explains the desire (not prediction) to fight the next war by essentially creating an early coup de main type battle and sweeping over the enemy nation so quickly they could not utilize their latent resources to build up large new formations of conscripts.

The French had a far different viewpoint, but one that also called for quick offensive action. The French stressed offense only, rapid attacks with overwhelming force at bayonet point. Their reasons were different from the Germans. The German desire to attack rapidly was born of fear of the ramifications of a massive general modern war between nations capable of equipping and fielding armies of millions for periods of years. The French were dominated by a need to make up for their ugly loss in the Franco-Prussian war, and obsessed with the idea that courage and elan would win the day. They also believed that the alliance with Russia (signed in 1892) would force the Germans to split their forces and allow them more freedom to engage offensively. The French planning was very unrealistic though. This is the nation that produced Napoleon, an artillery officer and whose armies were not only familiar with Napoleons tactical dependence on massed artillery but had recently acquired the French 75 cannon, one of histories great artillery pieces. They had also acquired the 1909 Mark I Hotchkiss machine gun, one of the greatest machine guns ever fielded. Yet in 1914 they went to war thinking they would fight an offensive war breaking German ranks with bayonet charges.

The British didn't matter so much, they were providing the Navy in this fight and the initial British Expeditionary Force was relatively small and symbolic. It does bear mentioning that the reason they weren't expected to figure into the war was the fact it was expected to take them a year to conscript, train, and field a sizable army.

The Russians were a confused mess. They had an army that was both obsolete and broken down on one hand, and undergoing a fairly radical attempt at modernization on the other. They had a decent infantry rifle going in, and were early adopters of radio technology and armored cars, the precursor to the tank. If they had had both of these in large numbers and with enough time to properly train in their use they probably would have rolled right over Germany. They very nearly did anyways, before being beat back by the Germans and bogging down into trench warfare, a long slow expensive war of attrition that shattered their fragile economy and political structure.

The Austrians were clueless. They weren't planning on war and weren't capable of fighting a war if one landed in their laps, which is essentially what happened to them. They were so out of touch that when they decided to send a punitive expedition to Serbia for the Serbian governments role in Archduke Franz Ferdinand's assassination they marched it right through the Serbian armies artillery training range, with predictable bad results.

To give this a tl;dr recap the 3 main competitors were the French Russians and Germans. The Germans essentially had the best idea of what was coming and tried for a quick win to avoid a long slow incredibly costly loss. The French were just nuts, planning on carrying the day with bayonet charges. The Russians had some great ideas but were 5-10 years away from being able to implement them properly. The British and Austrians, at least initially, were second rankers, and the Ottomans a side show.

What you got was fairly predictable. The Russians made a great charge that bogged down as soon as it ran into trouble (and Russian forces couldn't communicate effectively with each other). In the West the Germans kept trying to turn the French and British flank, the British and French kept regrouping and moving new troops further up the flank, and eventually the Germans ran out of land. Then you got von Moltke's dreaded war of attrition.

There are hundreds of books on this subject, I would recommend many but one recent one I have enjoyed is Peter Hart's The Great War. It gives a pretty good break down of political dispositions and the planning (and reasoning) of each armies prewar staff.