In many ways the war on the Western Front began as a fundamentally Franco-German conflict, and one with deep historical roots. The region had been of critical importance for French security for centuries. There is a similar continuity running across Franco-German conflicts from to , which helps to contextualize the war on the Western Front.
This vulnerability was contrasted against the immense financial, military and industrial strength of the united German state that arose out of the Franco-Prussian War. After , French diplomacy was largely concerned with preventing another crushing defeat at the hands of its strengthened neighbour. It was this imperative that led France to sign a defensive alliance with Russia in , thus setting the basic geographic parameters of the First World War twenty years before it began.
The alliance with Russia was awkward for a number of reasons. It also necessitated significant investment and financial aid for a Russian state still struggling to industrialize and modernize. This would ensure that Germany could not defeat its enemies one at a time, but would be forced to split its forces between two distant theatres, thus spreading its forces dangerously thin. To ensure that Russia would be able to mobilize quickly, France invested substantial sums to build new strategic railways that would better link the Russian heartland with its western border with Germany.
In these new rail lines were rapidly approaching completion. All of this put Germany in a very precarious position. Surrounded by hostile powers, Germany would very likely find itself fighting in a two-front war in the event of a general European conflict. Recognizing that it was unlikely to be able to prevail under such circumstances, Germany knew it would have to quickly overwhelm one of its enemies before turning to fight the other.
The pressure to quickly defeat one enemy compelled Germany to act swiftly and decisively. France had already mobilised, but was waiting within her borders for Germany to make the first move through the Low Countries. The next day Britain declared war on Germany, setting the stage for the war on the Western Front. This entailed the German attempt to sweep around the French left flank, take Paris from behind, and force France to capitulate in a matter of weeks.
