Is there any way that either side could've achieved a more decisive victory, early on, you think? Seems to me that the war bogged down as a result of Napoleonic tactics in an era of machine guns and modern artillery. Not a good combination, as the Battle of the Somme proved.
What if the "belligerents" had waited until 1918 to really make large offensives, using things like airplanes, tanks, flame throwers, gas, etc. in conjunction? Could've really handed it to the other side, had the other side primarily used the primitive tactics that the armies all demonstrated in 1914.
Would've been interesting to see how the M1919 machine gun did in the Trenches, as well as (if the war went on long enough) the M1921 Thompson.
Who were the main central powers in the War? There was Germany, the Austrio-Hungarian Empire (desperately trying to keep its mish-mash of nationalities, cultures, religions, and peoples under autocratic rule). I know the Turks fought with the Central Powers; was it still under the auspices of the Ottoman Empire?
The Allies were, primarily, the British Commonwealth, Belgium, France, Russia (until 1917), and the US. Though, "officially", China, Japan, and dozens of other countries were involved in the war as well. Italy was with the allies too, at least late in the war.