The Alliance System Leads to War

The war between Austria and Serbia might have been another “summer war,” like most European wars of the previous century. However, the carefully planned alliances soon drew the great powers into the conflict.

Russia and France Support Serbia

After receiving Austria's ultimatum, Serbia turned to its ally, Russia. From St. Petersburg, Nicholas II telegraphed William II. The tsar asked the kaiser to urge Austria to soften its demands. When this plea failed, Russia began to mobilize, or prepare its military forces for war. On August 1, Germany responded by declaring war on Russia.

Photo of men in military uniforms and bearskin caps carrying bayonets on horseback.

To aid its ally Serbia, Russia mobilized its army, including these Cossacks. As World War I began, European armies still sent cavalry units into battle.

Russia, in turn, appealed to its ally France. In Paris, nationalists saw a chance to avenge France's defeat in the Franco-Prussian War. Though French leaders had some doubts, they gave Russia the same kind of backing Germany offered to Austria. When Germany demanded that France keep out of the conflict, France refused. Germany then declared war on France.

Germany Marches Through Belgium

By early August, the battle lines were hardening. Italy and Britain still remained uncommitted. Italy chose to stay neutral for the time being. Neutrality is a policy of supporting neither side in a war. Britain had to decide quickly whether or not to support its ally France. Then, Germany's war plans suddenly made the decision for Britain.

Germany's worst fear was a war on two fronts, with France attacking from the west and Russia from the east. Years earlier, General Alfred Schlieffen (SHLEE fun) had developed a strategy to avoid a two-front war. Schlieffen reasoned that Russia's lumbering military would be slow to mobilize. Under the Schlieffen Plan, Germany first had to defeat France quickly. Then it would concentrate its forces against Russia.

To ensure a swift victory in the west, the Schlieffen Plan required German armies to march through neutral Belgium and then swing south behind French lines. The goal was to encircle and crush France's army. The Germans embarked on the plan by invading Belgium on August 3.

Photo of a field covered in flowed, through which an army of soldiers is marching.

In August 1914, Germany invaded neutral Belgium to reach France. Here, the German infantry advances across a Belgian field filled with flowers.

However, Germany had signed a treaty with Britain and France guaranteeing Belgian neutrality. Outraged by the invasion of Belgium, Britain declared war on Germany on August 4.

Once the machinery of war was set in motion, it seemed impossible to stop. Military leaders insisted that they must mobilize their forces immediately to accomplish their military goals.

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Table of Contents

World History Topic 1 Origins of Civilization (Prehistory–300 B.C.) Topic 2 The Ancient Middle East and Egypt (3200 B.C.–500 B.C.) Topic 3 Ancient India and China (2600 B.C.–A.D. 550) Topic 4 The Americas (Prehistory–A.D. 1570) Topic 5 Ancient Greece (1750 B.C.–133 B.C.) Topic 6 Ancient Rome and the Origins of Christianity (509 B.C.-A.D. 476) Topic 7 Medieval Christian Europe (330–1450) Topic 8 The Muslim World and Africa (730 B.C.-A.D. 1500) Topic 9 Civilizations of Asia (500–1650) Topic 10 The Renaissance and Reformation (1300–1650) Topic 11 New Global Connections (1415–1796) Topic 12 Absolutism and Revolution Topic 13 The Industrial Revolution Topic 14 Nationalism and the Spread of Democracy (1790–1914) Topic 15 The Age of Imperialism (1800–1914) Topic 16 World War I and the Russian Revolution (1914–1924) Topic 17 The World Between the Wars (1910–1939) Topic 18 World War II (1930–1945) Topic 19 The Cold War Era (1945–1991) Topic 20 New Nations Emerge (1945–Present) Topic 21 The World Today (1980-Present) United States Constitution Primary Sources 21st Century Skills Atlas Glossary Index Acknowledgments