History

War between the Central European Powers (Germany, Austria-Hungary, and allies) on one side and the Triple Entente (Britain and the British Empire, France, and Russia) and their allies, including the USA (which entered in 1917), on the other side.

1915, Allied expedition in World War I for the purpose of gaining control of the Dardanelles and Bosporus straits, capturing Constantinople, and opening a Black Sea supply route to Russia.

From Britannica Concise Encyclopedia
Major engagement of World War I between Germany and France. As part of its strategy of war by attrition, Germany selected the fortress of Verdun as the site it believed France would defend to the last man. After a massive bombardment, the Germans advanced with little opposition for four days before the reinforced French army under Philippe Pétain slowed their advance. For two months the hills west of the Meuse River and north of Verdun were bombarded, attacked, and counterattacked. By July, Germany, which was also engaged in the Battle of the Somme, had abandoned its strategy of attrition, and France gradually regained its forts and territory. The devastating losses included more than 400,000 French casualties and nearly as many German casualties.

From The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide
Battle zone in World War I between Germany and its enemies France and Britain, extending as lines of trenches from Nieuport on the Belgian coast through Ypres, Arras, Albert, Soissons, and Rheims to Verdun, constructed by both Germany and the Allies.

Agreement between two or more states to come to each other's assistance in the event of war. Alliances were criticized after World War I as having contributed to the outbreak of war, but the North Atlantic Treaty Organization (NATO) has been a major part of the post-1945 structure of international relations (as was the Warsaw Pact until its dissolution 1991).

In politics, the theory that the best way of ensuring international order is to have power so distributed among states that no single state is able to achieve a dominant position.

International organization formed after World War I to solve international disputes by arbitration. Established in Geneva, Switzerland, in 1920, the League included representatives from states throughout the world, but was severely weakened by the US decision not to become a member, and had no power to enforce its decisions.

Any of various gases sometimes used in warfare or riot control because of their poisonous or corrosive nature.

Person captured in war, who has fallen into the hands of, or surrendered to, an opponent.

The navy of Britain; In World War I its main task was to protect shipping from submarine attack.

A treaty that brought a formal end to the First World War.

A form of prolonged combat characterized by opposing systems of trenches from which each side launches assaults, patrols perimeters, and tries to shelter from enemy artillery and gunfire.

Offence (such as murder of a civilian or a prisoner of war) that contravenes the internationally accepted laws governing the conduct of wars, particularly the Hague Convention of 1907 and the Geneva Convention of 1949.