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Russia Mobilizes
Russia mobilizes its vast army to intervene against Austria-Hungary in favor of its ally, Serbia. This move starts a chain reaction that leads to the mobilization of the rest of the European Great Powers, and inevitably to the outbreak of hostilities. -
World War I Begins
Germany invades Belgium, beginning World War I. -
Germans Fire
The Germans fire shells filled with chlorine gas at Allied lines. This is the first time that large amounts of gas are used in battle, and the result is the near-collapse of the French lines. However, the Germans are unable to take advantage of the breach. -
Lusitania Sinks
A German submarine sinks the passenger liner Lusitania. The ship carries 1,198 people, 128 of them Americans. -
Germany Limits Submarines
Reacting to international outrage at the sinking of the Lusitania and other neutral passenger lines, Kaiser Wilhelm suspends unrestricted submarine warfare. This is an attempt to keep the United States out of the war, but it severely hampers German efforts to prevent American supplies from reaching France and Britain. -
First Tanks
The British employ the first tanks ever used in battle, at Delville Wood. Although they are useful at breaking through barbed wire and clearing a path for the infantry, tanks are still primitive and they fail to be the decisive weapon, as their designers thought they would be. -
Submarines Back
Germany resumes unrestricted submarine warfare in European waterways. This act, more than any other, draws the United States into the war and causes the eventual defeat of Germany. -
Zimmerman Telegram
British intelligence gives Wilson the so-called Zimmermann Telegram, a message from German foreign secretary Arthur Zimmermann proposing that Mexico side with Germany in case of war between Germany and the United States. In return, Germany promises to return to Mexico the "lost provinces" of Texas and much of the rest of the American -
U.S. Enters War
Congress authorizes a declaration of war against Germany. The United States enters World War I on the side of France and Britain. -
Battle of Cantigny
The Battle of Cantigny is the first major American offensive of the war. Though small in scale, the Americans fight bravely and soon go on to larger attacks against German positions. -
Battle of Belleau Wood
The Battle of Belleau Wood begins as the U.S. Marine Corps attacks the Germans across an open field of wheat, suffering huge casualties.
