Mobilization or mobilisation is the act of assembling and making both troops and supplies ready for war.
Intricate plans for mobilization contributed greatly to the beginning of World War I, since in 1914, under the laws and customs of warfare then observed (not to mention the desire to avoid compromising national security), general mobilization of one nation's military forces was invariably considered an act of war by that country's likely enemies. As the proverb claims, no army has ever mobilized without going to war.
In 1914, the United Kingdom was the only European Great Power without conscription. The other Great Powers (Austria-Hungary, France, Germany and Russia) all relied on compulsory military service to supply each of their armies with the millions of men they believed they would need to win a major war. Each of the Great Powers could only afford to keep a fraction of these men in uniform during peacetime, the rest were reservists with limited opportunities to train. Maneuvering formations of millions of men with limited military training required intricate plans which left no room for error, confusion or discretion after mobilization commenced. These plans were prepared under the assumption of worst-case scenarios.
For example, German military leaders did not plan to mobilize for war with Russia whilst assuming that France would not come to her ally's aid, or vice-versa. The Schlieffen Plan therefore dictated not only mobilization against both powers, but also the order of attack—France would be attacked first regardless of the diplomatic circumstances. To bypass the fortified Franco-German frontier, the German forces were to be ordered to march through Belgium. Whether or not Russia had committed the first provocation, the German plan called for the attack on Russia to take place only after France was defeated.
On July 28, 1914, Tsar Nicholas II of Russia ordered partial mobilization against Austria-Hungary. He ordered only partial mobilization because he was not at war with Germany, but Russian military plans at the time were based on the assumption that Russia would fight both Austria-Hungary and its ally Germany at the same time. Militarism was so strong that leaders of the military feared chaos if these plans were in any way changed, and so on July 29, 1914, the Tsar ordered full mobilization. For this reason Germany declared war on Russia.
Germany mobilized under the Schlieffen Plan, which assumed a two-front war with Russia and France. Like Russia, Germany decided to follow its two-front plans despite the one-front war. Germany declared war on France on August 3, 1914, one day after issuing an ultimatum to Belgium demanding the right of German troops to pass through as part of the planned pincer action of the military. Finally, Britain declared war on Germany for violating Belgian neutrality.
Thus the entangling alliances of the Triple Alliance and the Triple Entente directed the intricate plans for mobilization. This brought all of the Great Powers of Europe into the Great War without actually utilizing the provisions of either alliance.