Not at all certain. Communism was a strong presence in Europe before WWI and it is not at all certain that the transformation would have been peaceful all the way. Considering how the Czar behaved and how Russia was ruled it is easy to imagine a collapse of some sort even without the war.
Disagree. Communism was not a strong presence in Europe or anywhere else except as a fringe, intellectual movement. If anything it was in sharp decline by the 1900s, as social democrats and trade unionists began to more successfully represent the proletarians within the existing political order. This necessitated a radical reconfiguration of Marxist theory by thinkers such as Lenin, who then redefined the entire European population as a sort of imperial burgeoise living off of an expansionist, imperialistic capitalism. The real proletarians, in the new revised theory, were in the third world. Clearly, the revolution Marx predicted had failed; the working class conditions were improving and not declining, and the entire movement was fading away.
Then all of a sudden comes WWI. All of central and eastern Europe are thrown into a crisis. The old order completely demolishes itself in three years. Russia convulses under a liberal revolution, but the weak government is unable to resolve the war issue or end the chaos. Perfect timing for the Germans to transport the pacifist intellectual, Lenin, to Russia to impose his tragic intellectual "revolution" on the chaos, with his main promise being to end the war. When the government, the church, the civil society, and pretty much every pillar of traditional society throws the nation into the mass-homidical self-destruction that is war, a vacuum is created. When a vacuum is created, strange things come in and fill it. In this case, it was Marxism, and absurd intellectual dream more fitting for the 1840s than the 1910s. It never would have come close to happening without the war.
That is true. Still, one wonders what the course of history might have been like if some sort of diplomatic arbitrating strategy had worked out between Austria-Hungary and Serbia, and the "danger" presented by the collapse of the Ottoman Empire had not been allowed to lead to a wider war. The rest of the European map was much more stable, and it's possible to see a much more peaceful 20th century.