Greetings! This question certainly is one of those “what if?” ones which historians and military strategists studying the First World War have debated about even while the war was still in progress. To understand why Germany chose to fight a two-front war against France and Russia in the opening months of the conflict, we must first understand the conception of that plan which has so dominated the historiography on the German decision for war: the Schlieffen Plan. Let’s begin.

The “Great Symphony” of Schlieffen

“The offensive must never be allowed to come to a standstill.

- Historian Gerhard Ritter on the importance of speed in the German war plans of 1914.

When Alfred von Schlieffen was appointed as Chief of the General Staff of the German Army (1891-1906), he immediately departed from the traditional views on grand strategy that his predecessors had adopted: Russia first. Both Helmuth von Moltke the Elder and Alfred von Waldersee had the Russian “steam-roller” at the forefront of their concerns regarding Germany’s war plans, but the 1890s this concern about a war with Russia only had become a luxury, and a dangerous one to continue dreaming about. Just a year after his appointment, the Franco-Russian Alliance began to take shape, and Schlieffen realised that the prospect of a two-front war was becoming increasingly likely for Germany. As per the terms of the Alliance, Germany was envisioned as being the opponent of a combined Franco-Russian war effort:

1.If France is attacked by Germany, or by Italy supported by Germany, Russia shall employ all her available forces to attack Germany.

If Russia is attacked by Germany, or by Austria supported by Germany, France shall employ all her available forces to attack Germany.

2. In case the forces of the Triple Alliance, or of any one of the Powers belonging to it, should be mobilized, France and Russia, at the first news of this event and without previous agreement being necessary, shall mobilize immediately and simultaneously the whole of their forces, and shall transport them as far as possible to their frontiers.

3. The available forces to be employed against Germany shall be, on the part of France, 1,300,000 men, on the part of Russia, 700,000 or 800,000 men. These forces shall engage to the full with such speed that Germany will have to fight simultaneously on the East and on the West."

This thus led to Schlieffen having to adapt the German army’s plans to fighting a two-front war. With France and Russia, it no longer mattered which of the two Germany attacked or was attacked by, because the other would inevitably join the conflict as soon as it could mobilise. With this critical assumption, German army planners began to consider which of the two nations it would have to deal with first, before then shifting attention to the other. Historian Holger Herwig on the obstacles which Russia posed:

“Seen from Berlin, Russia constituted an inverted funnel. With every hundred miles they advanced, German armies would face an ever-widening front and the attendant need to administer ever-greater tracts of land and hostile populations. Spectacular but ultimately meaningless victories - what General Ludwig Beck later called ‘gusts of air’ - would bring no decision.”

Thus it was that Schlieffen arrived at his famous “France-first” strategy by 1892, and for the next decade he and his staff set to work planning how to avoid the French fortresses which lay on a line from Belfort to Dunkirk. In 1897, what would become the well-known basis for the Schlieffen plan was proposed: avoiding the fortresses by advancing around Luxembourg, southern Holland, and Belgium. In later revisions of the plan, this northern advance was narrowed down to Luxembourg and Belgium.

In the famous winter memoranda of 1905-1906, Schlieffen laid out his final operational concept. The bulk of the German army would mobilise around Aachen, breakthrough the Maastricht Appendix and the Ardennes forest, before wheeling through Belgium around the French forces and fortresses to the south, before then pushing into the Seine basin to push the french forces onto the anchored German forces in Lorraine. This Kesselschlacht (battle of encirclement), was designed to give the Germans the best chance of securing a rapid victory. Just forty-two days was given to carry out the entire plan, a best-case scenario. In the east, Russia would be held at bay by a much smaller force, deflecting any offensives and holding off the “colossus” until victory in the west could enable the transfer of troops to the east.

By 1913, Moltke the Younger had taken over Schlieffen’s role, and he made adjustments to the Schlieffen Plan which ruled out other key options. The Germans did have a plan for mobilising against Russia first, and launching an offensive there whilst a smaller force defended the western border with France. This plan, embodied in the Aufsmarch Ost I and Aufsmarch Ost II files, were shelved by Moltke in 1913 after he concluded that an isolated war with Russia was practically impossible, and that France would be easier to defeat.

For more on why the Schlieffen-Moltke Plan was carried out in its final form as it was in 1914, see this earlier writeup of mine.

OP’s Points

Let us now then turn to the points which OP has put forth in their explanatory boilerplate to the question.

The first point is definitely a valid one. The British would have been far less inclined to declare war on Germany had the question of Belgian neutrality remained intact. If Germany put up a defensive force on its border with France and began offensive operations into Russia only, this would removed part of the casus belli for Britain. However, we must remember that the German general staff in 1914 was very much afraid of the alternative which a defensive war with France implied: a drawn out conflict, in which the swift victories imagined by Schlieffen and Moltke were all but impossible to achieve. The Second Reich was not the Third; total mobilization was a policy which no-one wanted to enact. In other words, Germany could not afford to be fighting a protracted war against two powers which were materially and militarily equivalent to her in 1914 (at least by sheer numbers). Hence Schlieffen's insistence that speed was of the essence, and that the German army had a better chance of defeating France first rather than Russia.

Secondly, although Russia was certainly see as militarily inferior to Germany in 1914, this perception only assisted with the argument for war. In 1913, Russia had just enacted several programmes to expand her army, update its equipment, and prepare further railways for rapid mobilisation. The German army staff and civilian leadership feared that if Russia was allowed to complete these expansions by the scheduled year (1917), then they would stand absolutely no chance of winning a war against her. Thus, in the July Crisis, this turned into a “now or never” clause for Moltke. If Germany allowed Russia’s “Great Program” of army expansion and modernization to continue, then the result would be disastrous for her military fortunes in wartime. As late as May 1914, Moltke voiced such concerns to Secretary of State von Jagow:

“The prospects for the future weighed heavily upon him [Moltke]. In two or three years Russia would have finished arming. Our enemies’ military power would then be so great he did not know how he could deal with it. Now we were still more or less a match for it. In his view there was no alternative but to fight a preventive war so as to beat the enemy while we could still emerge fairly well from the struggle.”

Thirdly, whilst the domestic reasons for a push into Russia certainly seem logical, we must not forget that Russia was by no means a “weak” enemy. All this talk of inferiority and equal forces is entirely relative. In terms of absolute numbers, Russia’s army was vastly larger than Germany’s, not to mention the sheer size of the Russo-German frontier and the difficulty of consolidating any territorial gains while also defending against France. We ought to turn this argument around: if Germany’s offensive against Russia failed, and brought on a war of attrition, then German revolution was also a possibility. Schlieffen feared such an event in his planning, writing about avoiding the “red ghost” of socialist revolution due to a drawn-out war. Further, a German attack into Russia would have likely united the Russian populace against a common enemy, perhaps stalling the revolution until the external threat was eliminated.

So there we have it. The offensive against Russia first has been discussed by historians and military strategists in the decades following the Great War. The arguments outlined above reflect some of their conclusions: that the Schlieffen Plan brought with it many assumptions in the military planning of a two -front war, that an offensive against Russia first would drag out the conflict, and that 1914 appeared to be a better time than any to tackle the Franco-Russian alliance.

Hope this response helps, and feel free to ask any follow-ups as you see fit.