World War I, military
conflict, from August 1914 to November 1918, that involved many of the
countries of Europe as well the United States and other nations throughout the
world. World War I was one of the most violent and destructive wars in European
history. Of the 65 million men who were mobilized, more than 10 million were
killed and more than 20 million wounded. The term World War I did not
come into general use until a second worldwide conflict broke out in 1939 (see
World War II). Before that year, the war
was known as the Great War or the World War.
World War I was the first total war. Once the war began,
the countries involved mobilized their entire populations and economic
resources to achieve victory on the battlefield. The term home front,
which was widely employed for the first time during World War I, perfectly
symbolized this new concept of a war in which the civilian population behind
the lines was directly and critically involved in the war effort.
The war began as a clash between two coalitions of
European countries. The first coalition, known as the Allied Powers, included
the United Kingdom, France, Belgium, Serbia, Montenegro, and the Russian Empire (see
Russia). The Central Powers, which opposed
them, consisted of the empires of Germany and Austria-Hungary. Japan joined the Allied Powers in 1914.
The Ottoman Empire joined the Central Powers
in 1914, as did Bulgaria in 1915. The same year, Italy entered the war on the Allied side.
Although the United States initially remained neutral,
it joined the Allies in 1917. The conflict eventually involved 32 countries, 28
of which supported the Allies. Some of these nations, however, did not
participate in the actual fighting.
The immediate cause of the war was the assassination of
Archduke Francis Ferdinand, the heir to the throne
of