| Term | Definition |
| Militarism | The policy involving aggressively building up a nation's armed forces in preparation for war and giving military more authority over the government and foreign policy |
| Mobilization | The readying of troops for war |
| Central Powers | In World War I, Germany and Austria-Hungary |
| Allies | In World War I, Russia, France, Serbia, and Great Britain |
| Stalemate | A situation in which neither side in conflict is able to gain the advantage |
| Propaganda | Information intended to sway public opinion |
| U-Boat | A German Submarine |
| Sussex Pledge | Pledge be the German government in 1916 that its submarines would warn ships before attacking |
| Zimmerman Note | A telegram sent by Germany's foreign secretary in 1917 to Mexican officials proposing an alliance with Mexico and promising U.S. territory if Mexico declared war on the United States |
| Autocrat | Ruler with unlimited power |
| Russian Revolution | Collapse of the czar's government in Russia in 1917, after which the Russian monarchy was replaced with a republican government |
| Selective Service Act | Law passed in 1917 authorizing a draft of young men for military service in World War I |
| American Expeditionary Force (AEF) | Name given to American troops in Europe in World War I |
| Convoy | Group of unarmed ships surrounded by a ring of armed naval ships |
| Zeppelin | A German floating airship |
| Armistice | A cease-fire or truce |
| Genocide | Organized killing of an entire people |
| Liberty Loans/Bonds | Special war bond sold by the government to support the Allied cause during World War I |
| Price Controls | System of pricing determined by the government |
| Rationing | Distributing goods to consumers in a fixed amount |
| Daylight Savings Time | Turning clocks ahead by one hour for the summer |
| Sedition | Any speech or action that encourages rebellion |
| Vigilante | A citizen who takes the law into his or her own hands |
| Fourteen Points | President Wilson's proposal in 1918 for postwar European Peace |
| Self Determination | The power to make decisions about one's own future |
| Spoils | Rewards gained through military victory |
| League of Nations | International organization formed after World War I that aimed to ensure security and peace for all its member |
| Patriotism | Love of one's country |
| Reparations | Payment from an enemy for economic injury suffered during a war |
| Big Four | Woodrow Wilson (US president), Georges Clemenceau of France, David Lloyd George of Britain, Vittorio Orlando of Italy |
| Versailles Treaty | 1919 treaty that ended World War I |
| Archduke Francis Ferdinand | Heir to the throne of Austria-Hungary assassinated by Gavrilo Princip |
| Gavrilo Princip | Assassinated Archduke Francis Ferdinand because he believed that Bosnia should be part of neighboring Serbia, not Austria-Hungary |
| Von Schlieffen Plan | Germany's plan to avoid Two-Front War |
| Henry Cabot Lodge | Massachusetts senator who was against the League of Nations |
| Eugene Debs | Socialist and former presidential candidate who drew a ten-year jail sentence for criticizing the American government and business leaders and for urging people to "resist militarism" |
| Robert Prager | German-born citizen who was lynched by a mob for enlisting in the navy |
| George Creel | Headed the Committee on Public Information, for promoting the war effort in WWI |
| Herbert Hoover | Worked to aid Europeans during World War I |
| Bernard Baruch | He headed the War Industries Board which placed the control of industries into the hands of the federal government |
| Alvin York | American soldier who was awarded the Congressional Medal of Honor for bravery during World War I |
| John J. Pershing | Leader of the American Expeditionary Forces during World War I |
| Arthur Zimmerman | A German foreign secretary that had secretly proposed a German- Mexican alliance in the Zimmerman Note |