20th century

== Summary ==
At the beginning of the period, the [[British Empire]] was the world's most powerful nation,<ref name="ferguson">{{Cite book |last=Ferguson |first=Niall |year=2004 |title=Empire: The rise and demise of the British world order and the lessons for global power |publisher=Basic Books |location =New York |isbn=978-0-465-02328-8}}</ref> having [[Pax Britannica|acted as the world's policeman]] for the past century.

[[File:World_1914_empires_colonies_territory.PNG|thumb|750px|center|{{center|World powers and empires in 1914, just before the First World War.  }}]]

Technological advancements during [[World War I]] changed the way war was fought, as new inventions such as [[tank]]s, [[chemical weapons]], and aircraft modified tactics and strategy. After more than four years of [[trench warfare]] in Western Europe, and up to 22 million dead, the powers that had formed the [[Triple Entente]] ([[French Third Republic|France]], [[United Kingdom of Great Britain and Ireland|Britain]], and [[Russian Empire|Russia]], later replaced by the United States and joined by [[Kingdom of Italy|Italy]] and [[Kingdom of Romania|Romania]]) emerged victorious over the [[Central Powers]] ([[German Empire|Germany]], [[Austria-Hungary]], the [[Ottoman Empire]] and [[Kingdom of Bulgaria|Bulgaria]]). In addition to annexing many of the [[Colony|colonial possessions]] of the vanquished states, the Triple Entente exacted punitive restitution payments from them, plunging Germany in particular into [[Hyperinflation in the Weimar Republic|economic depression]]. The Austro-Hungarian and Ottoman empires were dismantled at the war's conclusion. The [[Russian Revolution]] resulted in the overthrow of the [[Tsar]]ist regime of [[Nicholas II]] and the onset of the [[Russian Civil War]]. The victorious [[Bolsheviks]] then established the [[Soviet Union]], the world's first [[communist state]].

[[File:League of Nations Anachronous Map.PNG|thumb|Anachronous world map showing [[member states of the League of Nations]], the first [[Global governance|global international body of governance]] created to prevent war after [[World War I]], during its 26-year [[interwar period]] history.]]

[[Fascism]], a movement which grew out of post-war [[angst]] and which accelerated during the [[Great Depression]] of the 1930s, gained momentum in [[Italian Fascism|Italy]], [[Nazism|Germany]], and [[Falangism|Spain]] in the 1920s and 1930s, culminating in [[World War II]], sparked by [[Nazi Germany]]'s aggressive expansion at the expense of its neighbors. Meanwhile, [[Empire of Japan|Japan]] had rapidly transformed itself into a technologically advanced industrial power and, along with Germany and Italy, formed the [[Axis powers]]. Japan's military [[expansionism]] in East Asia and the Pacific Ocean brought it into conflict with the United States, culminating in [[Attack on Pearl Harbor|a surprise attack]] which drew the US into World War II.

[[File:Bundesarchiv Bild 101I-020-1268-36, Russland, russischer Gefallener, Panzer BT 7,.jpg|thumb|Ukraine, early days of the 1941 [[Operation Barbarossa|Nazi invasion]]. The [[Soviet Union]] lost around 27 million people between 1941 and 1945,<ref>Mark Harrison (2002). ''[https://books.google.com/books?id=yJcD7_Q_rQ8C&pg=PA167 Accounting for War: Soviet Production, Employment, and the Defence Burden, 1940–1945]''. Cambridge University Press. p. 167. {{ISBN|0-521-89424-7}}</ref> almost half of all [[World War II casualties|World War II deaths]].]]

After some years of dramatic military success, Germany was [[German Instrument of Surrender|defeated]] in 1945, having been [[Western Allied invasion of Germany|invaded]] by the [[Soviet Union]] and [[Polish Armed Forces in the East|Poland]] [[Eastern Front (World War II)|from the East]] and by the United States, the United Kingdom, Canada, and [[Free France|France]] [[Western Front (World War II)|from the West]]. After the victory of the [[Allies of World War II|Allies]] in Europe, the [[Pacific War|war in Asia]] ended with the [[Soviet invasion of Manchuria]] and the [[Atomic bombings of Hiroshima and Nagasaki|dropping of two atomic bombs]] on Japan by the US, the first nation to develop [[nuclear weapons]] and the only one to use them in warfare. In total, World War II left some 60 million people dead.

[[File:Atomic cloud over Hiroshima - NARA 542192 - Edit.jpg|thumb|left|The [[mushroom cloud]] of the detonation of [[Little Boy]], the [[Atomic bombings of Hiroshima and Nagasaki|first nuclear attack]] in history, on 6 August 1945 over [[Hiroshima]], igniting the [[nuclear age]] with the international security dominating thread of [[mutual assured destruction]] in the latter half of the 20th century.]]

Following World War II, the United Nations, successor to the [[League of Nations]], was established as an international forum in which the world's nations could discuss issues diplomatically. It enacted [[United Nations resolution|resolutions]] on such topics as the conduct of warfare, environmental protection, international [[sovereignty]], and human rights. [[Peacekeeping]] forces consisting of troops provided by various countries, with various United Nations and other aid agencies, helped to relieve famine, disease, and poverty, and to suppress some local armed conflicts. Europe slowly united, economically and, in some ways, politically, to form the [[European Union]], which consisted of 15 European countries by the end of the 20th century.

After the war, Germany was [[Allied-occupied Germany|occupied]] and divided between the [[Western Bloc|Western]] powers and the Soviet Union. [[East Germany]] and the rest of [[Eastern Bloc|Eastern Europe]] became Soviet [[puppet states]] under communist rule. Western Europe was rebuilt with the aid of the American [[Marshall Plan]], resulting in a major [[Post–World War II economic expansion|post-war economic boom]], and many of the affected nations became close allies of the United States.

With the Axis defeated and Britain and France rebuilding, the United States and the Soviet Union were left standing as the world's only superpowers. Allies during the war, they soon became hostile to one another as their competing ideologies of [[communism]] and [[democratic capitalism]] proliferated in Europe, which became divided by the [[Iron Curtain]] and the [[Berlin Wall]]. They formed competing military alliances ([[NATO]] and the [[Warsaw Pact]]) which engaged in a decades-long standoff known as the [[Cold War]]. The period was marked by a [[Nuclear arms race|new arms race]] as the USSR became the second nation to develop nuclear weapons, which were produced by both sides in sufficient numbers to [[Nuclear holocaust|end most human life on the planet]] had a large-scale nuclear exchange ever occurred. [[Mutual assured destruction|Mutually assured destruction]] is credited by many historians as having prevented such an exchange, each side being unable to [[Pre-emptive nuclear strike|strike first]] at the other without ensuring an equally devastating [[Second strike|retaliatory strike]]. Unable to engage one another directly, the conflict played out in a series of [[proxy war]]s around the world—particularly in [[Chinese Civil War|China]], [[Korean War|Korea]], [[Cuban revolution|Cuba]], [[Vietnam War|Vietnam]], and [[Soviet–Afghan War|Afghanistan]]—as the USSR sought to [[World communism|export communism]] while the US attempted to [[Containment|contain it]]. The technological competition between the two sides led to substantial investment in [[research and development]] which produced innovations that reached far beyond the battlefield, such as [[Space Race|space exploration]] and the Internet.

[[File:Africa independence dates.PNG|thumb|The international community grew in the second half of the century significantly due to a new wave of decolonization, particularly in Africa. Most of the newly independent states, were grouped together with many other so called [[developing countries]]. Developing countries gained attention, particularly due to rapid population growth, leading to a record [[world population]] of nearly 7&nbsp;billion people by the end of the century.]]

In the latter half of the century, most of the [[History of colonialism|European-colonized world]] in Africa and Asia gained independence in a process of [[decolonization]]. Meanwhile, [[globalization]] opened the door for several nations to exert a strong influence over many world affairs. The US's global military presence spread [[Culture of the United States|American culture]] around the world with the advent of the [[Cinema of the United States|Hollywood motion picture industry]] and [[Broadway theatre|Broadway]], [[jazz]], rock music, and pop music, fast food and [[hippy]] counterculture, [[hip-hop]], [[house music]], and [[disco]], as well as [[street style]], all of which came to be identified with the concepts of popular culture and [[youth culture]].<ref>{{cite web |last1=Delaney |first1=Tim |title=Pop Culture: An Overview |url=https://philosophynow.org/issues/64/Pop_Culture_An_Overview |website=Philosophy Now |access-date=12 September 2022}}</ref><ref>{{cite journal |last1=Bell |last2=Bell |first1=P. |first2=R. |title="Americanization": Political and cultural examples from the perspective of "Americanized" Australia |journal=American Studies |date=1996 |url=https://core.ac.uk/download/pdf/162640366.pdf |access-date=12 September 2022}}</ref><ref>{{cite book |last1=Malchow |first1=Howard |title=Special Relations: The Americanization of Britain? |date=2011 |publisher=Stanford University Press |isbn=978-0-804-77399-7}}</ref> After [[Dissolution of the Soviet Union|the Soviet Union collapsed]] under internal pressure in 1991, most of the communist governments it had supported around the world [[Revolutions of 1989|were dismantled]]—with the notable exceptions of China, [[North Korea]], [[Cuba]], [[Vietnam]], and [[Laos]]—followed by awkward transitions into market economies.