World War I and the Russian Revolution 1915-1925
History

A security arrangement in which each state in the system accepts that the security of one is the concern of all
Collective security
A security arrangement in which each state in the system accepts that the security of one is the concern of all. Collective security. In history, collective security refers to countries working together to prevent conflict by agreeing to defend each other against potential aggressors.

A group of troopships traveling together with a naval escort
Convoy system
A group of troopships traveling together with a naval escort. Convoy system. The convoy system was a strategy used during wartime to protect merchant ships from enemy attacks by grouping them together with naval escorts for safety.

The naval operations of UK, France, Russia and Australia against the Ottoman Empire
Dardanelles campaign
The naval operations of UK, France, Russia, and Australia against the Ottoman Empire. Dardanelles campaign. The Dardanelles campaign was a failed World War I military effort by the Allies to secure a sea route to Russia.

A British ocean liner that was sunk by a German U-boat, this contributed to the American entry into WWI
Lusitania
A British ocean liner that was sunk by a German U-boat, this contributed to the American entry into WWI. Lusitania. The Lusitania was a British passenger ship sunk by Germany in 1915, which helped push the U.S. into World War I.

The class of workers in urban areas who work in industry or manufacturing
Proletariat
The class of workers in urban areas who work in industry or manufacturing. Proletariat. In history, the proletariat refers to the working-class people who sell their labor for wages, especially during the industrial revolution.

The right of a people to choose their sovereignty and international political status
Self-determination
The right of a people to choose their sovereignty and international political status. Self-determination. In history, self-determination is when a group decides its own government and future, often after being a colony or under foreign rule.