I know about the von Schlieffen plan. But what I don't understand is why Germany thought that it needed to invade anyone while the trouble was between Austria and her Serbian Protectors.
There are some indications that Germany was becoming seriously worried about Russia's rapid recovery from the events of 1905 (both the loss to Japan and the internal revolution) and felt that the clock was ticking toward the day when Russia would become invincible against Germany. So, while caught up in the immediate need to support Austria against the Serbs, there is a good possiblity Germany had one monocled eye cocked on Russia for reasons that went well beyond her pan-Slavic tendency to succor the Serbs.
So, if this was at all about Russia, then it was inevitably about France, which made it about Belgium. Indeed, diplomatically speaking, the hip bone was connected to the thigh bone was connected to the knee bone . . . .
I think it's important to survey the situation as it had evolved during Kaiser Wilhelm's reign. During most of Bismarck's tenure, the diplomatic map of Europe looked something like this:
- Britain was largely neutral in continental affairs but occasionally in conflict with France over both their colonial dominions. (This was one of the reasons Bismarck studiously resisted pressure to venture into Africa and westward, where he would inevitably run afoul of Britain, France, Belgium, and the Netherlands. Hence his famous nostrum, "my map of Africa lies in Europe.")
- Britain and France shared a centuries-long antipathy that made cooperation between them on other matters difficult and transitory.
- Germany was aligned with Russia and Austria-Hungary through the Three Emperors League. They were viewed as natural allies both by virture of their similar political attitudes and by their lack of colonial aspirations that would put them in contention with each other outside of the European theater. (This was the other reason Bismarck shied away from colonial aspirations, where any designs in the Pacific rim would put him on a collision course with Russia.)
The first crack in this German diplomatic armor was when the Three Emperors League fell apart over the Alexander von Battenberg affair in Bulgaria. Bismarck hastily cemented a new defensive alliance with Russia in the Reinsurance Treaty of 1887. When Wilhelm dismissed the 75-year-old Bismarck in 1890, Wilhelm stupidly failed to grasped the importance of renewing this treaty, driving a now-isolated Russia into the arms of France.
While all this was going on, France and Britain were begining to turn their tenuous 1881 overtures to each other into a serious wooing. This resulted in marriage in 1904 with the Entente Cordiale, which was a sweeping set of accords that defused the colonial issues that had been constant irritants and occasional triggerpoints between them. Then Russia joined in 1907, thereby encircling Germany in a mesh of diplomatic understandings which even brought the United States, Spain, and Japan into alignment against Germany in some scenarios.
Then, as if all this weren't bad enough, Wilhelm began making noises about colonial aspirations -- which, given the fact that all the good stuff was already taken, was certain to make the U.S., western Europe, and Russia nervous -- and he began making more than noise about building a Germany navy to support those aspirations -- certain to drive Britain to a distraction of worry. (One has to remember that Britain, a tiny island nation of virtually no consequence as a land power, had become a major world power by amplifying herself via her navy into a global empire.)
So -- in a nutshell -- if Germany was to have any hope of dealing with Russia at all, she had to take France out of the equation. Hence the march through Belgium. If only old Herr von Schlieffen had gotten it right, much of 20th-century history would have gone very differently.