World
War I (WWI) was a global war centred in Europe that began on 28 July
1914 and lasted until 11 November 1918. It was predominantly called the
World War or the Great War from its occurrence until the start of World
War II in 1939, and the First World War or World War I thereafter. It
involved all the world's great powers,[5] which were assembled in two
opposing alliances: the Allies (based on the Triple Entente of the
United Kingdom, France and Russia) and the Central Powers (originally
centred around the Triple Alliance of Germany, Austria-Hungary and
Italy; but, as Austria–Hungary had taken the offensive against the
agreement, Italy did not enter into the war).[6] These alliances both
reorganised (Italy fought for the Allies), and expanded as more nations
entered the war. Ultimately more than 70 million military personnel,
including 60 million Europeans, were mobilised in one of the largest
wars in history.[7][8] More than 9 million combatants were killed,
largely because of technological advancements that led to enormous
increases in the lethality of weapons without corresponding improvements
in protection or mobility. It was the sixth-deadliest conflict in world
history, subsequently paving the way for various political changes such
as revolutions in many of the nations involved.[9]
Long-term causes
of the war included the imperialistic foreign policies of the great
powers of Europe, including the German Empire, the Austro-Hungarian
Empire, the Ottoman Empire, the Russian Empire, the British Empire, the
French Republic, and Italy. The assassination on 28 June 1914 of
Archduke Franz Ferdinand of Austria, the heir to the throne of
Austria-Hungary, by a Yugoslav nationalist in Sarajevo, Bosnia and
Herzegovina was the proximate trigger of the war. It resulted in a
Habsburg ultimatum against the Kingdom of Serbia.[10][11] Several
alliances formed over the previous decades were invoked, so within weeks
the major powers were at war; via their colonies, the conflict soon
spread around the world.
On 28 July, the conflict opened with the
Austro-Hungarian invasion of Serbia,[12][13] followed by the German
invasion of Belgium, Luxembourg and France; and a Russian attack against
Germany. After the German march on Paris was brought to a halt, the
Western Front settled into a static battle of attrition with a trench
line that changed little until 1917. In the East, the Russian army
successfully fought against the Austro-Hungarian forces but was forced
back from East Prussia and Poland by the German army. Additional fronts
opened after the Ottoman Empire joined the war in 1914, Italy and
Bulgaria in 1915 and Romania in 1916. The Russian Empire collapsed in
March 1917, and Russia left the war after the October Revolution later
that year. After a 1918 German offensive along the western front, the
Allies drove back the German armies in a series of successful offensives
and United States forces began entering the trenches. Germany, which
had its own trouble with revolutionaries at this point, agreed to a
cease-fire on 11 November 1918, later known as Armistice Day. The war
had ended in victory for the Allies.
Events on the home fronts were
as tumultuous as on the battle fronts, as the participants tried to
mobilize their manpower and economic resources to fight a total war. By
the end of the war, four major imperial powers—the German, Russian,
Austro-Hungarian and Ottoman empires—ceased to exist. The successor
states of the former two lost a great amount of territory, while the
latter two were dismantled entirely. The map of central Europe was
redrawn into several smaller states.[14] The League of Nations was
formed in the hope of preventing another such conflict. The European
nationalism spawned by the war and the breakup of empires, the
repercussions of Germany's defeat and problems with the Treaty of
Versailles are agreed to be factors contributing to World War II