WWI: exactly how did it start?

If you step back and look at what you wrote, this is a truly odd position to take, but does exemplify the bizarre ‘logic’ that went into the Von Schlieffen plan, German thinking, and the politics that caused WWI to happen. Yes, France wanted revenge for 1870-71, wanted Alsace-Lorraine back, and enthusiastically went off to war in 1914, but every nation enthusiastically went off to war in 1914, something that may seem hard to comprehend today. Germany was extremely interested in fighting France; so interested in fact that Germany had no plans for a war with only Russia. The only reason Germany ‘had’ to declare war on France is because the only war plans they had drawn up required them to do so - from the moment general mobilization was ordered, the only choice left to be made was which version of the modified Schlieffen plan to put into effect, and the only difference between them was what percentage of the German army was to be deployed to the east in the delaying action against Russia. As soon as mobilization went into effect and the trains started moving, the carefully drawn up train schedules would start delivering German troops to the Franco-Belgian-Luxemburg borders which German troops would then immediately begin marching across, violating Belgian and Luxemburg neutrality. The ultimatum that Germany delivered to France was written to be entirely unacceptable and to be rejected, leading to a German declaration of war. If for some bizarre reason France had accepted the demands of the German ultimatum, Germany would have found itself in the extremely embarrassing position of having violated the neutrality of and having gone to war with Belgium when word of French acceptance of German demands arrived.

IIRC this was true for Russia too: their mobilization plan was against both Austria-Hungary and Germany. When Austria attacked Serbia and Russia was about to declare war on Austria, the czar asked his generals to mobilize against Austria only, but the generals told him that they have plans only for a full mobilization.

Yes and no. Yes, Russia could either fully mobilize or not at all; there was no plan to partially mobilize only against Austria. However, and it’s a big however, Russia ordering general mobilization didn’t in and of itself set the wheels of war irreversibly in motion. Russian general mobilization didn’t automatically send the Russian army marching into East Prussia the way German general mobilization did automatically send the German army marching into Belgium and Luxemburg. Russia ordering mobilization led to Germany ordering mobilization, which led to the full scale outbreak of war, but Russian general mobilization didn’t mean war with Germany was unavoidable and diplomacy no longer an option. Germany ordering general mobilization meant it was going to war with France, period, regardless of what caused it, and it was going to do so by invading neutral Belgium. Diplomacy was a moot point the instant Germany mobilized, the extent of German diplomacy consisted of ultimatums intended to be rejected, demands that countries allow their neutrality to be violated without putting up a fight (which again wasn’t considered remotely plausible), and a declaration of war with Russia so ham handed that Russia was handed both versions of the declaration of war by accident; one version for declaring war because Russia had refused German demands and the other for declaring war because they hadn’t replied to Germany’s demands quickly enough. It wasn’t just that Germany couldn’t order a partial mobilization; Germany had only one war plan and it went into effect the moment the orders for general mobilization were signed. German mobilization meant war, and it meant war with France. The German army was already marching through Belgium and Luxemburg when they declared war on France.

Germany ended up declaring war on Russia and France - supposedly in defense of its Austrian ally - at a time when neither country had declared war on Austria. As I wrote in a previous post, Germany wanted a general war and used Austria (which didn’t) as an excuse.

[QUOTE=Dissonance]
German general mobilization did automatically send the German army marching into Belgium and Luxemburg. Russia ordering mobilization led to Germany ordering mobilization, which led to the full scale outbreak of war, but Russian general mobilization didn’t mean war with Germany was unavoidable and diplomacy no longer an option.
[/QUOTE]

   Indeed, Germany's mobilization was purely offensive, while Russia's not necessarily so. But the reason I've mentioned Russia's "all or nothing" mobilization  is because it shows that military planners of all major powers were planning for a generalized war. There were no plans for limited conflicts. This made sense from military point of view, but apparently the civilian leaders of the respective countries were not fully aware of this. 
  At least that's the impression I got from MacMillan's book: the politicians were not really aware that a limited show of force was not an option. IIRC, both the czar and the kaiser asked (before the actual war declarations) if a limited mobilization against only one enemy was possible, only to be be told "no way dude!" by their respective military chiefs. 

 I think that during the Cold War the civilian leadership was very aware of what military options were on the table and the risks involved in using them.

The problem was that Germany’s entire war plan was based on the idea of mobilization being the equivalent of a declaration of war. Their plan was based on the premise that they could mobilize faster than France and much faster than Russia. So they would mobilize and invade and defeat France before the French were able to mobilize their forces and then turn around and invade and defeat Russia before the Russians were able to mobilize their forces. The whole plan treated mobilization as a race with the winner being the side they finished it first - the actual battles were treated as an epilogue.

So the Germans figured they couldn’t just mobilize. If everyone was mobilizing but not following through with invasions, they would end up in a situation where they would face a fully mobilized France and Russia and they didn’t think they could defeat a fully mobilized France and Russia.

The same situation would arise fifty years later in the nuclear war planning between the United States and Soviet Union. Each side realized that getting in a first strike would be a huge advantage. So planning went in to not only how to launch an attack but also how to launch an attack quicker than the other side.

There’s an inherent instability in situations where each side knows it will gain a decisive advantage by striking first. You can have a political situation where neither side really wants a war but each side feels driven to anticipate the possibility that the other side might launch an attack.

This reached a zenith with the introduction of MIRVs.

Assuming that one MIRVed-missile carries 10 warheads, that one missile can take out 10 of the enemy’s missiles (before the latter have launched). But, each one of those enemy missiles carries its 10 warheads. So, by striking first you can theoretically remove 100 enemy warheads (10 X 10) with just one of your missiles - an extremely tempting proposition.

You can get trapped in an escalating cycle of trying to outguess your opponent. You’re thinking about the possibility of launching a pre-emptive strike. So you have to realize your opponent must be thinking about the advantage he would gain by launching a pre-emptive first strike. And each of you knows that the other side is aware of your awareness of what they’re thinking.

“If he’s going to launch his attack in ten minutes, I should pre-empt him by launching my attack in five minutes. But he’s going to know I’ll try to pre-empt his attack in five minutes so he’ll move his launch up and attack in two minutes. And if he’s going to launch his attack in two minutes, I should be hitting the launch button RIGHT NOW!”

The declaration of war is just weird. It reads like they’re proposing a duel or something.

I love the German communication to Belgium too :

[QUOTE=Germany]
The German Government would, however, feel the deepest regret if Belgium regarded as an act of hostility against herself the fact that the measures of Germany’s opponents force Germany, for her own protection, to enter Belgian territory.
[/QUOTE]