So, for whatever reason you choose (perhaps the assassination plot against Franz Ferdinand fails, perhaps cooler heads prevail among European diplomats, perhaps something else), no World War I in 1914. What happens?
Some things to consider:
1) Home Rule in Ireland? It's been debated here before about what would happen, about how the public would react; still, it's worth mentioning.
2) Tank development? Armored cars were already beginning to be integrated into armies; at what point would armored, armed tractors start joining them? Without the Great War, how would tank and armored-car designs evolve?
3) The Rifians? Considering earlier German plots in Morocco, I'd be shocked if Germany didn't try to supply any Rifian revolt.
4) The Augsleich? It was due for renegotiation in 1917.
5) The 'war poets' and 'war novelists' and other literary-types whose careers were directly impacted by the Great War? Would any of them be likely to go into literature anyways?
5b) Dada? Dada was strongly influenced by the Great War, though the fin-de-siecle mood pervading Europe also contributed. Without the war, though, how does it develop? On the other hand, might the lack of war help spread a Dada-like movement faster, since there wouldn't be closed borders between France and Germany?
6) Airplanes? No Great War means no massive production runs of aircraft, no large-scale training programs, no base of trained pilots to fuel 1920s aviation. How much does the lack of a Great War slow developments in aviation?
7) Flu? No Great War means that the 'Spanish' flu can't spread among the troops... but it can still spread like an ordinary epidemic. Thoughts?
8) Kaiserliche Marine? How long could Germany keep up the naval arms race with Britain, and to what extent was it interested in doing so?
9) Colonies? No Great War means no mass usage of colonial levies, no large-scale debts run up by the war. How much longer could colonialism last?
10) Diplomacy? How long before a major war would break out in Europe, even if the one in 1914 was avoided?
Feel free to address any or all of these questions, along with any other thoughts you have about how history might've proceeded without the Great War.