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World War I (1914–1919)


Key Terms

terms Key Terms


Allied Powers

An alliance during World War I that originally consisted of Russia, France, and Britain. Many other countries, including Belgium, Canada, Greece, Italy, Japan, and Romania, joined later as associate powers. Although the United States never joined the Allied Powers—preferring on principle to fight the Central Powers independently—it cooperated closely with the Allied Powers once it joined the war in 1917.

Austria’s Ultimatum to Serbia

An ultimatum that Austria issued to Serbia on July 23, 1914, escalating tensions between the two nations. The ultimatum demanded that Serbia crack down on anti-Austrian propaganda in the Serbian press and that Serbia allow Austria to participate directly in judicial proceedings to prosecute the parties guilty of assassinating Archduke Franz Ferdinand.

Battle of the Bight

A battle on August 28, 1914, in which the British Royal Navy baited German warships in Helgoland Bight out to sea, where British forces sank three of the German ships with few losses of their own.

Battle of Coronel

A November 1, 1914, engagement in which the German East Asia Squadron defeated a weaker British squadron off the coast of Argentina.

Battle of the Falkland Islands

A battle on December 8, 1914, in which the British decimated the German East Asia Squadron during an attack on the Falkland Islands in the South Atlantic.

Battle of Gallipoli

A lengthy campaign, lasting from April 25, 1915, to January 6, 1916, in which Britain invaded Turkey’s Gallipoli Peninsula as part of its effort to force open the Dardanelles, the strait between Europe and Asia. The operation failed and cost hundreds of thousands of lives before the British abandoned the operation and evacuated their forces at the start of 1916.

Battle of the Marne

A battle on September 59, 1914, in which Allied forces, following their retreat from Mons, stopped German forces on the banks of the Marne River and forced them back forty-five miles to the river Aisne.

Battle of the Masurian Lakes

An engagement on September 914, 1914, in which two German armies under the command of General Paul von Hindenburg defeated Russia’s First Army under General Paul von Rennenkampf. Russia suffered 125,000 casualties.

Battle of Messines Ridge

An intensive June 7, 1917, assault by the British on German forces in northern France. The British began preparations six months in advance, digging nineteen tunnels under a ridge where the Germans were entrenched and then filling the tunnels with explosives. The operation was a success and forced the Germans to retreat.

Battle of Mons

A battle on August 23, 1914, that was one of the earliest battles on the western front. The German advance in Belgium overwhelmed British and French forces, who began a fourteen-day retreat to the outskirts of Paris.

Battle of Passchendaele

An engagement lasting from September 20 to October 12, 1917, in which British forces in Belgium continued to push the Germans back. The fighting was especially miserable because it was carried out during a period of heavy rains.

Battle of the Somme

One of the largest battles of the war, fought in northern France from July 1 to November 18, 1916, simultaneously with the Battle of Verdun. The Battle of the Somme was the result of an Allied offensive along a twenty-five-mile front. Although it ended up as a small victory for the Allied Powers, it cost them 146,000 lives in order to advance less than six miles.

Battle of Tannenberg

A battle in Prussia (present-day Poland) on August 2630, 1914, in which two German armies under command of General Paul von Hindenburg engaged Russia’s Second Army under General Alexander Samsonov. It was a catastrophic defeat for Russia, which suffered over 120,000 casualties.

Battle of Verdun

The longest and one of the deadliest battles of the war, lasting from February 21 to December 18, 1916. Germany, hoping to wear France down and inflict large numbers of casualties, assaulted the fortified town of Verdun, which blocked the German forces’ path to Paris. The battle ended without a clear victor, despite the deaths of more than 650,000 soldiers.

Black Hand

A terrorist Serbian nationalist group that was responsible for training and arming Gavrilo Princip and others who participated in the assassination of Archduke Franz Ferdinand.

“Blank Check”

Kaiser Wilhelm II of Germany’s unconditional promise to defend Austria-Hungary if Russia attacked it while Austria was invading Serbia. The guarantee was made on July 5, 1914, a week after Archduke Ferdinand’s assassination.


Technically, the term for the total number of people who are killed, wounded, or captured in a battle. Use of this word varies, but historians generally follow this convention.

Central Powers

An alliance during World War I that originally consisted of Germany and Austria-Hungary. Other nations, including Bulgaria and the Ottoman Empire, joined later.

Schlieffen Plan

A German military plan, formulated in 1905, that addressed how Germany should handle the threat of a war on two fronts with Russia and France. In short, the plan stipulated that if war were expected, Germany should first attack France before embarking upon military actions against Russia. The rationale for this approach was that Russia would require several weeks in order to mobilize its troops and assemble them along the German border. Under the plan, Germany hoped to overrun France in only six weeks by attacking across France’s borders with Belgium and Holland, which were less fortified than the border with Germany.

Triple Alliance

A prewar alliance among Germany, Austria-Hungary, and Italy, formalized in 1882. At the start of World War I, Italy dropped out of this alliance, initially maintaining a neutral position in regard to the war.

Triple Entente

A vaguely defined prewar alliance among Russia, France, and Britain, finalized in 1907. The Triple Entente was not a formal treaty and had little real substance.

War of Attrition

A war in which victory is determined purely by which side is better able to endure numerous, prolonged casualties (as opposed to a war in which victory is determined by accomplishing a specific objective, such as capturing a major city).

Zimmermann Telegram

A January 1917 telegram sent by German foreign minister Alfred Zimmermann to the German ambassador to Mexico, discussing a secret plan to bait Mexico into attacking the United States. Under the plan, Germany intended to offer Mexico financial incentives to attack the United States, as well as military support to help Mexico retake its former territories of Texas, New Mexico, and Arizona. British intelligence intercepted the telegram, which was eventually published in the American press, sparking an uproar that shifted American public opinion in favor of entering the war.

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