The argument of Source C is reinforced by Source E which is equally emphatic in stressing that the Schlieffen Plan made War inevitable due to its inflexibility. It meant that Germany had no choice but to implement its Schlieffen Plan just as soon as “Russia even mobilised;” Source E however also implies that it was German incursion into Belgian territory, i.e. the “transgression” of Belgian neutrality which caused “almost all of the Great Powers” to be involved in the First World War. Source E is hence more comprehensive than Source C in explaining the main cause of the War. From contextual knowledge, I understand that it was because of the German’s incursion into Belgian territory that brought England into the War. At the Treaty of Westminster in 1839 Britain had promised to uphold and was therefore committed, to defend Belgium if it was ever attacked. The title of book, “The War Plans of the Great Powers 1880-1914” implies that its author was an expert in the field of military strategies. Hence I would tend to think that this published source is both accurate and true.
Source D. written by another military strategist, Winston Churchill, too supports Source C, in that the German army “must storm Liege”. Churchill points out that the bombing of Liege “destroyed all chance” that a peaceful negotiation could avert the War. Source D further supports Source E in explaining how the execution of the Schlieffen plan meant the inevitability of war, because it necessitated the violation of Belgian neutrality. Source D went further; Churchill hinted that war was already inevitable at the first instance of mobilization; “Mobilisation therefore spelt war”. According to contextual knowledge, Russia was the first country to mobilize, and when she refused to back down after warning by Germany to do so, the Schlieffen Plan swung into action. Apart from blaming the war on “military plans” Churchill hinted that the ignorance of contingencies of military planning on the part of the sovereigns contributed to the War. I would say that this source is accurate and believable based on the fact that it corroborated with my readings. Moreover, Churchill was an expertise in military strategies and theories and the source was written with the privilege of hindsight in 1931.
Source B is the least useful of the sources that “support” the hypothesis. It explains how King Leopold of Belgium was unable to affirm if he “…would take her stand on…” the side of the Germans, i.e., to allow the Germans safe passage through Belgium. It did not state in as bold a manner that the neutrality of Belgian would be compromised, except that Germany could not “guarantee” that Belgian territory would be safe from German attack. Whether King Leopold knew what this meant exactly is not clear in the source, but contextual knowledge points out clearly that the fortification of the Liege was meant specifically for that purpose. So looking at Source D again, I would think that Churchill may not be right in painting the monarchs of Europe as rather ignorant sovereigns. Source B appears to take Germany to task for demanding that Leopold should “should give him (the Kaiser) a written declaration…Belgium would take her stand on our (Germany’s side) otherwise Belgian might be invaded and the King hence would lose his kingdom. The provenance however alludes to the fact that the source was but a “report” of a conversation with the Kaiser William II 1904. It is not stated when the “report” was actually written, hence the report may not be totally accurate due to lapses of memory. In that sense, Source B is not as useful as Sources C, D and E, in showing “support” for the hypothesis.
Source A does not address the hypothesis at all. It is only source that does not refer to the military plans of Germany explicitly. However from contextual knowledge, we know that the author of the source, the elder von Moltke, had recommended that Russia be dealt with first in case of a two-front war faced by Germany. The fact that the source was a “speech to the Reichstag” tells us that it is a credible source. It points to the fact that Germany was still defensive in her foreign policy in 1890 and seems to imply that she was cautious about being involved in a large scale war, since “ …no end to it can be foreseen.. ... and woe to him that sets fire to Europe.” Unfortunately by the time the First World War took place, the elder Moltke was no longer around to advise caution.
On the whole most of the sources, B, C, D and E all support to a certain extent the hypothesis that “German military planning made it impossible” for her accept a peaceful solution. In terms of “support” for the hypothesis, Source C with its explicit and direct reference to the Schileffen Plan Plan, is the most useful. Source A is the least useful, because it did not refer to the contingencies of the Schlieffen Plan. In fact it contradicts the hypothesis, implying that Germany was aware of the dangers of a large scale conflict. It is also least useful because it was referring to foreign policy of Germany before the adoption of Weltpolitik by German leaders.
Based on my readings, I understand tend to believe that it was the “blank cheque” or the unequivocal support given by Germany to Austria, pressing the latter for immediate mobilization against Russia that was the main cause of the First World War. However the crucial consideration of military momentum as a result of advance planning and a desire not to lose the race of mobilization made the war inevitable. While the Germans had their Schlieffen Plan, the Germans had their Plan XVII, hence the hypothesis might be better phrased as "Military planning of all countries, principally that of Germany’s Schleiffen Plan, made it impossible for a peaceful solution to the diplomatic crisis of July 1914." Obviously, the set of given sources could then include reference to France’s Plan XVII.
Comments: The parts in blue have been included/edited
Notes on Plan XVII
Technically, Plan XVII called for an advance by four French Armies into Alsace-Lorraine on either side of the Metz-Thionville fortresses, occupied by the Germans since 1871. The southern wing of the invasion forces would first capture Alsace and Lorraine (in that order), whilst the northern wing would - depending upon German movements - advance into Germany via the southern Ardennes forests, or else move north-east into Luxembourg and Belgium.
The architects of Plan XVII, which included Joseph Joffre, took little account of a possible German invasion of France through Belgium until just before war was declared; and in modifying the plan to deploy troops to meet such an eventuality, actual French activity to meet an invasion via Belgium was lacklustre at best in August 1914.