Mobilization (or mobilisation in British English) 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 1 or The Great War. In 1914, at the time of World War 1, the act of mobilization was considered an act of war.

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, and 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 and brought all of the Great Powers of Europe into the Great War.