The world war of 1914 to 1918 involved most of the world’s major powers. It was a global conflict that began in Europe but spread to Africa and Asia and even into the oceans as submarine warfare became common. It was a result of many trends including nationalism, increased militarism and imperial rivalry and competition for power.

A series of events led to the outbreak of war in Europe in early August 1914. The assassination of Archduke Franz Ferdinand by Serbian nationalists triggered an escalation of tensions between the Austro-Hungarian and Russian empires. Then Germany invaded neutral Belgium on their way to France, provoking Britain to join the conflict. The Allied and Central Powers had vastly different demographic, industrial and military resources, which created the basis for the rival system of opposing alliances that developed over the previous 35 years.

Imperialism fueled the war as many of the warring nations had colonies that contributed troops to their mother countries, which sought to expand their territory and control over raw materials. In addition, a new technology of aircraft opened up the possibility of air warfare.

By the end of the war, more than 65 million men volunteered or were conscripted to fight in mass citizen armies. Millions of civilians also contributed to the war effort by working in factories or on farms and in support services, such as food and supplies for the fighting forces. This was a brutal and deadly war that lasted four years and left an indelible mark on the planet.