The United Kingdom declares war on Germany, after Germany invades Belgium
Austria-Hungary declares war on Russia and Serbia declares war on Germany
U.S. President Woodrow Wilson announces the U.S. will remain neutral
The First Battle of the Marne begins. Trench warfare begins as soldiers on both sides dig in.
Battle of Ypres begins
The unofficial Christmas truce is declared.
Germany declares a "war zone" around Great Britain, essentially effecting a submarine blockade where even neutral merchant vessels were to be potential targets.
The Second Battle of Ypres begins. It is during this battle that the Germans first use poison gas.
The British ocean liner RMS Lusitania is sunk by German U-boat, U-20
The Battle of Verdun begins. The Battle of Verdun was the longest battle of World War I and was one of the bloodiest.
The Battle of the Somme begins. During the Battle of the Somme, tanks are first introduced into battle.
Germany sends the secret Zimmerman Telegram to Mexico in an effort to entice Mexico to join the war. The British intercept and decipher the coded message.
The United States declares war on Germany.
Russia signs the Treaty of Brest Litovsk, which is a peace treaty between Russia and the Central Powers.
German Kaiser Wilhelm II abdicates and flees Germany.
Germany signs the armistice at Compiegne, France. Fighting ends on the 11th hour of the 11th day of the 11th month