Allied Powers - An alliance between a number of countries including Britain, France, Russia, Italy, and Japan. The Allied Powers fought against the Central Powers in World War I. The U.S. fought on the same side of the Allies, but called itself an "associated" power.
Armistice - An agreement by both sides to stop fighting while a peace treaty is negotiated.
Artillery - Large, heavy guns used on land warfare.
Balkans - A geographical region in Southeast Europe that includes countries such as Bulgaria, Croatia, Greece, Romania, and Serbia.
Big Four - The Big Four were the leaders from the four Major Allies including Britain, France, Italy, and the United States. The US, Britain, and France were sometimes referred to as the Big Three.
Blockade - An effort to prevent goods and/or people from entering or leaving a country.
Bolsheviks - A faction of the communist Marxist Party in Russia that gained power during the Russian Revolution.
Central Powers - The Central Powers included Germany, Austria-Hungary, the Ottoman Empire, and Bulgaria. They fought against the Allied Powers in World War I.
Conscript - A person who is enlisted into the army whether they want to join or not.
Christmas Truce - the Christmas Truce was an unofficial cease fire between the two sides of World War I on Christmas. In some cases the soldiers from each side met, talked, played soccer, and exchanged gifts.
Doughboy - The nickname for US soldiers in World War I.
Duckboards - Boards placed on the bottom of trenches to keep the soldier's feet dry and out of the water or mud.
Dreadnought - Dreadnoughts were large and heavily armored battleships.
Fourteen Points - President Woodrow Wilson issued Fourteen Points that were his goals for an end to World War I and lasting peace.
Eastern Front - The Eastern Front during World War I was fought in Eastern Europe between Germany, Austria-Hungary, and Bulgaria on one side and Russia and Romania on the other side.
Front line - The front line was the point at which the armies of each side met. This is where most of the fighting took place.
Kaiser - The Kaiser was the German Emperor.
League of Nations - The League of Nations was formed after World War I. It was a group of governments that strived to prevent wars and protect independent nations. It was replaced by the United Nations after World War II.
Lusitania - The Lusitania was a large luxury passenger ship that was sunk by a German submarine. Over 1,000 passengers were killed.
Mobilize - To mobilize is to gather and prepare an army for war.
No Man's Land - The area between the front lines of two enemy armies was called No Man's Land.
Outflank - To move around the side of an enemy in battle.
Pacifist - Someone who is against war and fighting for any reason.
Pals battalions - The Pals battalions were units in the British Army that grouped men who were friends and had enlisted together.
Propaganda - Information used and distributed to present one side of an issue.
Prussia - A geographical region of the German Empire that included northern Germany and Poland.
Reparations - Payment that the losers of a war must pay to the victors.
Schlieffen Plan - A strategy that Germany had for fighting a war on two fronts: one against France and one against Russia.
Treaty of Brest-Litovsk - A peace treaty between the Central Powers and Russia. After the Russian Revolution the new communist government wanted out of the war and made peace with Germany.
Treaty of Versailles - The Treaty between the Allies and Germany that ended World War I.
Trench warfare - A type of land warfare where each side digs long lines of trenches for protection. Much of the western front during World War I was fought for years using trench warfare.
Triple Entente - The original alliance between Russia, France, and Britain. It later became the Allied Powers.
U-boat - The name for German submarines which comes from the German word "Unterseeboat."
Western front - The region of fighting that took place in Western Europe between Germany and Austria-Hungary on one side and France, Britain, and (later) the United States on the other.
Zimmerman Telegram - A secret telegram from Germany that was intercepted by the British. It requested an alliance between Germany and Mexico against the United States. The discovery of this telegram caused the United States to declare war on Germany.