> - Field Marshal Alfred von Schlieffen writes a plan which becomes the sacred text of how the German army is to conduct a two front war against France and Russia. One of the critical parts of that plan is marching a truly massive German army through neutral Belgium.

> - When France Germany and Russia go to war Germany following the Schlieffen plan marches through Belgium triggering UK involvement in the war.

Neither of these points are true. Schlieffen produced several different war plans for different potential scenarios and in WW1 Germany wound up following a very heavily modified version of one of those plans. While Britain officially gave the violation of Belgian neutrality as its reason for entering the war, and it certainly swayed public opinion in favor of the conflict, they had signed a treaty with France in 1911 pledging military support in the event of a German invasion regardless; and more generally had been in an increasingly antagonistic relationship with Germany for years.

Perhaps had Schlieffen not been so obsessed with Cannae he would have made different recomendations, but the fact is that the rest of the German general staff generally agreed with the logic behind those recomendations. Then when their plans were put into action, they were largely vindicated as the invasion through Belgium did allow Germany to gain a massive advantage in the opening weeks of the war and sieze territory from which it would take years and millions of men to dislodge them. Indeed the main issue was that the plan assumed Russia would be slow to mobilize, giving the German army time to defeat France before they would have to reposition forces to the eastern front, but to everyone's surprise Russia instead mobilized quickly. A generation later, when the men who were boots on the ground at the time now led the German military, and had decades to study the previous conflict, they decided on attempting a plan that was broadly similar and again had great initial success.

It's possible that Germany employs a totally different strategy in WW1 if Schlieffen isn't obsessed with Cannae, but there's no real evidence that they would.

Not really.

The causes of WWI are complex, but the simplest summary is that the great powers of Europe reached a point where a war between any two of them would necessitate a war between all of them. To argue that Schlieffen contributed to WWI, you need to first argue that Schlieffen is the only thing that makes the German military believe it can win a two front war (which I think reverses cause and effect), and also argue that a German military believing that a two-front war is unwinnable would have caused the German government to work assiduously to keep war from breaking out (which I find unbelievable, given the tenor of Wilhelm's foreign policy).

In the actual event, Belgium doesn't play a major role in Britain's entry into the war (it's an easier sell than "diplomatic reasons we haven't exactly been telling you about" though, which is why it's played up so heavily). But look at a topographic map of Europe, and you'll realize that the easiest route from Germany to France is to go through northern Belgium [1], avoiding the more difficult terrain of eastern France. Even absent the specific Schlieffen plan, it's likely that German war plans would involve going through Belgium anyways, especially if your goal is as rapid a capture of Paris as possible.

If you look at the history of German war plans against France, essentially every modification is about pulling yet more troops from the invasion through Belgium to other sectors of the war, whether it be somewhere on the Eastern Front, or the direct border with France. This is really at odds with the mythologization of the Schlieffen plan, and I suspect that some of that myth-making comes from the apparent near-success of the German advance on Paris. People can look at how close it came to Paris and think that, had only Moltke not diverted yet another division of troops elsewhere, the Germans could have made it. Ignoring the fact that it failed because German logistics was literally keeling over dead [2], and pushing any more Germans into that army would have broken the logistics system faster.

[1] Incidentally, probably the biggest blow to the "original" Schlieffen plan (the actual war plans change considerably over time) is removing the plan to also march through the Dutch province of Limbourg, which now requires the entire Germany army to squeeze through a 12 mile gap near Liège.

[2] This of course referring to horse-drawn wagons, with the horses dying from overwork.