Confusion among the Central Powers
The strategy of the Central Powers suffered from miscommunication. Germany had promised to support Austria-Hungary's invasion of Serbia, but interpretations of what this meant differed. Previously tested deployment plans had been replaced early in 1914, but never tested in exercises. Austro-Hungarian leaders believed Germany would cover its northern flank against Russia. Germany, however, envisioned Austria-Hungary directing the majority of its troops against Russia, while Germany dealt with France. This confusion forced the Austro-Hungarian Army to divide its forces between the Russian and Serbian fronts.
On 9 September 1914, the Septemberprogramm, a possible plan which detailed Germany's specific war aims and the conditions that Germany sought to force upon the Allied Powers, was outlined by German Chancellor Theobald von Bethmann-Hollweg. It was never officially adopted.
Some of the first clashes of the war involved British, French and German colonial forces in Africa. On 7 August, French and British troops invaded the German protectorate of Togoland. On 10 August, German forces in South-West Africa attacked South Africa; sporadic and fierce fighting continued for the remainder of the war. The German colonial forces in German East Africa, led by Colonel Paul Emil von Lettow-Vorbeck, fought a guerrilla warfare campaign for the duration of World War I, only surrendering two weeks after the armistice took effect in Europe.
The Serbian army fought the Battle of Cer against the invading Austro-Hungarians, beginning on 12 August, occupying defensive positions on the south side of the Drina and Sava rivers. Over the next two weeks Austrian attacks were thrown back with heavy losses, which marked the first major Allied victory of the war and dashed Austro-Hungarian hopes of a swift victory. As a result, Austria had to keep sizeable forces on the Serbian front, weakening its efforts against Russia.
German forces in Belgium and France
At the outbreak of the First World War, the German army (consisting in the West of seven field armies) executed a modified version of theSchlieffen Plan, designed to quickly attack France through neutral Belgium before turning southwards to encircle the French army on the German border. The plan called for the right flank of the German advance to converge on Paris and initially, the Germans were very successful, particularly in the Battle of the Frontiers (14–24 August). By 12 September, the French with assistance from the British forces halted the German advance east of Paris at the First Battle of the Marne (5–12 September). The last days of this battle signified the end of mobile warfare in the west. The French offensive into Germany launched on 7 August with the Battle of Mulhouse had limited success.
In the east, only one Field Army defended East Prussia and when Russia attacked in this region it diverted German forces intended for the Western Front. Germany defeated Russia in a series of battles collectively known as the First Battle of Tannenberg (17 August – 2 September), but this diversion exacerbated problems of insufficient speed of advance from rail-heads not foreseen by the German General Staff. The Central Powers were thereby denied a quick victory and forced to fight a war on two fronts. The German army had fought its way into a good defensive position inside France and had permanently incapacitated 230,000 more French and British troops than it had lost itself. Despite this, communications problems and questionable command decisions cost Germany the chance of obtaining an early victory.
Asia and the Pacific
New Zealand occupied German Samoa (later Western Samoa) on 30 August. On 11 September, the Australian Naval and Military Expeditionary Force landed on the island of Neu Pommern (later New Britain), which formed part of German New Guinea. Japan seized Germany's Micronesian colonies and, after the Siege of Tsingtao, the German coaling port of Qingdao in the Chinese Shandong peninsula. Within a few months, the Allied forces had seized all the German territories in the Pacific; only isolated commerce raiders and a few holdouts in New Guinea remained.