World War I[b] or the First World War (28 July 1914 – 11 November 1918), also known
as the Great War, was a global conflict between two coalitions: the Allies (or
Entente) and the Central Powers. Fighting took place mainly in Europe and the
Middle East, as well as in parts of Africa and the Asia-Pacific, and in Europe was
characterised by trench warfare; the widespread use of artillery, machine guns, and
chemical weapons (gas); and the introductions of tanks and aircraft. World War I
was one of the deadliest conflicts in history, resulting in an estimated 10 million
military dead and more than 20 million wounded, plus some 10 million civilian dead
from causes including genocide. The movement of large numbers of people was a major
factor in the deadly Spanish flu pandemic.
The causes of World War I included the rise of Germany and decline of the Ottoman
Empire, which disturbed the long-standing balance of power in Europe, as well as
economic competition between nations triggered by industrialisation and
imperialism. Growing tensions between the great powers and in the Balkans reached a
breaking point on 28 June 1914, when a Bosnian Serb named Gavrilo Princip
assassinated Archduke Franz Ferdinand, heir to the Austro-Hungarian throne.
Austria-Hungary held Serbia responsible, and declared war on 28 July. After Russia
mobilised in Serbia's defence, Germany declared war on Russia and France, who had
an alliance. The United Kingdom entered after Germany invaded Belgium, whose
neutrality it guaranteed, and the Ottomans joined the Central Powers in November.
Germany's strategy in 1914 was to quickly defeat France, then to transfer its
forces to the east, but its advance was halted in September, and by the end of the
year the Western Front consisted of a continuous line of trenches stretching from
the English Channel to Switzerland. The Eastern Front was more dynamic, but neither
side gained a decisive advantage, despite costly offensives. Italy, Bulgaria,
Romania, Greece and others joined in from 1915 onward.
In April 1917, the United States entered the war on the Allied side following
Germany's resumption of unrestricted submarine warfare against Atlantic shipping.
Later that year, the Bolsheviks seized power in the Russian October Revolution, and
Soviet Russia signed an armistice with the Central Powers in December, followed by
a separate peace in March 1918. That month, Germany launched an offensive in the
west, which despite initial successes left the German Army exhausted and
demoralised. A successful Allied counter-offensive from August 1918 caused a
collapse of the German front line. By early November, Bulgaria, the Ottoman Empire
and Austria-Hungary had each signed armistices with the Allies, leaving Germany
isolated. Facing a revolution at home, Kaiser Wilhelm II abdicated on 9 November,
and the war ended with the Armistice of 11 November 1918.
The Paris Peace Conference of 1919–1920 imposed settlements on the defeated powers,
most notably the Treaty of Versailles, by which Germany lost significant
territories, was disarmed, and was required to pay large war reparations to the
Allies. The dissolution of the Russian, German, Austro-Hungarian, and Ottoman
Empires redrew national boundaries and resulted in the creation of new independent
states, including Poland, Finland, the Baltic states, Czechoslovakia, and
Yugoslavia. The League of Nations was established to maintain world peace, but its
failure to manage instability during the interwar period contributed to the
outbreak of World War II in 1939.
