World War II

===Background===
{{Main|Causes of World War II}}

====Aftermath of World War I====
{{stack|[[File:Bundesarchiv Bild 102-09042, Genf, Völkerbund, Sitzungssaal.jpg|thumb|The [[League of Nations]] assembly, held in [[Geneva]], [[Switzerland]] (1930).]]}}
[[World War I]] had radically altered the political European map with the defeat of the [[Central Powers]]—including [[Austria-Hungary]], [[German Empire|Germany]], [[Kingdom of Bulgaria|Bulgaria]], and the [[Ottoman Empire]]—and the 1917 [[October Revolution|Bolshevik seizure of power]] in [[Russian Republic|Russia]], which led to the founding of the Soviet Union. Meanwhile, the victorious [[Allies of World War I]], such as France, Belgium, Italy, Romania, and Greece, gained territory, and new [[Nation state|nation-states]] were created out of the dissolution of the Austro-Hungarian, Ottoman, and Russian Empires.<ref>{{cite web |last1=Mintz |first1=Steven |title=Historical Context: The Global Effect of World War I |url=https://www.gilderlehrman.org/history-resources/teaching-resource/historical-context-global-effect-world-war-i |website=The Gilder Lehrman Institute of American History |access-date=4 March 2024 |archive-date=4 March 2024 |archive-url=https://web.archive.org/web/20240304193001/https://www.gilderlehrman.org/history-resources/teaching-resource/historical-context-global-effect-world-war-i |url-status=live }}</ref>

To prevent a future world war, the [[League of Nations]] was established in 1920 by the [[Paris Peace Conference (1919–1920)|Paris Peace Conference]]. The organisation's primary goals were to prevent armed conflict through collective security, military, and [[Washington Naval Treaty|naval disarmament]], as well as settling international disputes through peaceful negotiations and arbitration.<ref>{{cite news |last1=Gerwarth |first1=Robert |title=Paris Peace Treaties failed to create a secure, peaceful and lasting world order |url=https://www.irishtimes.com/culture/heritage/paris-peace-treaties-failed-to-create-a-secure-peaceful-and-lasting-world-order-1.3745849 |newspaper=The Irish Times |access-date=29 October 2021 |language=en |archive-date=14 August 2021 |archive-url=https://web.archive.org/web/20210814213229/https://www.irishtimes.com/culture/heritage/paris-peace-treaties-failed-to-create-a-secure-peaceful-and-lasting-world-order-1.3745849 |url-status=live }}</ref>

Despite strong pacifist sentiment [[Aftermath of World War I|after World War{{nbsp}}I]],{{sfn|Ingram|2006|pp=[{{GBurl|id=bREQibN9i-sC|p=76}} 76–78]}} [[Irredentism|irredentist]] and [[Revanchism|revanchist]] [[nationalism]] had emerged in several European states. These sentiments were especially marked in Germany because of the significant territorial, colonial, and financial losses imposed by the [[Treaty of Versailles]]. Under the treaty, Germany lost around 13 percent of its home territory and all [[German colonial empire|its overseas possessions]], while German annexation of other states was prohibited, [[World War I reparations|reparations]] were imposed, and limits were placed on the size and capability of the country's [[Reichswehr|armed forces]].{{sfn|Kantowicz|1999|p=149}}

====Germany====
The German Empire was dissolved in the [[German Revolution of 1918–1919]], and a democratic government, later known as the [[Weimar Republic]], was created. The interwar period saw strife between supporters of the new republic and hardline opponents on both the political right and left. Italy, as an Entente ally, had made some post-war territorial gains; however, Italian nationalists were angered that the [[Treaty of London (1915)|promises made]] by the United Kingdom and France to secure Italian entrance into the war were not fulfilled in the peace settlement. From 1922 to 1925, the [[Italian fascism|Fascist]] movement led by [[Benito Mussolini]] seized power in Italy with a nationalist, [[Totalitarianism|totalitarian]], and [[class collaboration]]ist agenda that abolished representative democracy, repressed socialist, left-wing, and liberal forces, and pursued an aggressive expansionist foreign policy aimed at making Italy a world power, promising the creation of a "[[New Roman Empire]]".{{sfn|Shaw|2000|p=35}}

[[File:Nürnberg Reichsparteitag Hitler retouched.jpg|thumb|upright|right|[[Adolf Hitler]] at a German [[Nazism|Nazi]] political rally in [[Nuremberg]], August 1933]]
[[Adolf Hitler]], after an [[Beer Hall Putsch|unsuccessful attempt to overthrow the German government]] in 1923, eventually [[Adolf Hitler's rise to power|became the Chancellor of Germany]] in 1933 when [[Paul von Hindenburg]] and the Reichstag appointed him. Following Hindenburg's death in 1934, Hitler proclaimed himself ''Führer'' of Germany and abolished democracy, espousing a [[New Order (Nazism)|radical, racially motivated revision of the world order]], and soon began a massive [[German rearmament|rearmament campaign]].{{sfn|Brody|1999|p=4}} France, seeking to secure its alliance with Italy, [[Franco-Italian Agreement of 1935|allowed Italy a free hand in Ethiopia]], which Italy desired as a colonial possession. The situation was aggravated in early 1935 when the [[Territory of the Saar Basin]] was legally reunited with Germany, and Hitler repudiated the Treaty of Versailles, accelerated his rearmament programme, and introduced conscription.{{sfn|Zalampas|1989|p=62}}

====European treaties====
The United Kingdom, France and Italy formed the [[Stresa Front]] in April 1935 in order to contain Germany, a key step towards [[Military globalization|military globalisation]]; however, that June, the United Kingdom made an [[Anglo-German Naval Agreement|independent naval agreement]] with Germany, easing prior restrictions. The Soviet Union, concerned by Germany's [[Drang nach Osten|goals of capturing vast areas of Eastern Europe]], drafted a treaty of mutual assistance with France. Before taking effect, though, the [[Franco-Soviet Treaty of Mutual Assistance|Franco-Soviet pact]] was required to go through the bureaucracy of the League of Nations, which rendered it essentially toothless.<ref>{{Harvnb|Mandelbaum|1988|p=96}}; {{Harvnb|Record|2005|p=50}}.</ref> The United States, concerned with events in Europe and Asia, passed the [[Neutrality Acts of the 1930s|Neutrality Act]] in August of the same year.{{sfn|Schmitz|2000|p=124}}

Hitler defied the Versailles and [[Locarno Treaties]] by [[Remilitarisation of the Rhineland|remilitarising the Rhineland]] in March 1936, encountering little opposition due to the policy of [[appeasement]].{{sfn|Adamthwaite|1992|p=52}} In October 1936, Germany and Italy formed the [[Axis powers|Rome–Berlin Axis]]. A month later, Germany and Japan signed the [[Anti-Comintern Pact]], which Italy joined the following year.{{sfn|Shirer|1990|pp=298–299}}

====Asia====
The [[Kuomintang]] (KMT) party in China launched a [[Northern Expedition|unification campaign]] against [[Warlord Era|regional warlords]] and nominally unified China in the mid-1920s, but was soon embroiled in [[Chinese Civil War|a civil war]] against its former [[Chinese Communist Party]] allies{{sfn|Preston|1998|p=104}} and [[Central Plains War|new regional warlords]]. In 1931, an [[Statism in Shōwa Japan|increasingly militaristic]] [[Empire of Japan]], which had long sought influence in China{{sfn|Myers|Peattie|1987|p=458}} as the first step of what its government saw as the country's [[Hakkō ichiu|right to rule Asia]], staged the [[Mukden incident]] as a pretext to [[Japanese invasion of Manchuria|invade Manchuria]] and establish the [[puppet state]] of [[Manchukuo]].{{sfn|Smith|Steadman|2004|p=28}}

China appealed to the [[League of Nations]] to stop the Japanese invasion of Manchuria. Japan withdrew from the League of Nations after being [[Lytton Report|condemned]] for its incursion into Manchuria. The two nations then fought several battles, in [[January 28 incident|Shanghai]], [[Battle of Rehe|Rehe]] and [[Defense of the Great Wall|Hebei]], until the [[Tanggu Truce]] was signed in 1933. Thereafter, Chinese volunteer forces continued the resistance to Japanese aggression in [[Pacification of Manchukuo|Manchuria]], and [[Actions in Inner Mongolia (1933–1936)|Chahar and Suiyuan]].<ref>{{Harvnb|Coogan|1993}}: "Although some Chinese troops in the Northeast managed to retreat south, others were trapped by the advancing Japanese Army and were faced with the choice of resistance in defiance of orders, or surrender. A few commanders submitted, receiving high office in the puppet government, but others took up arms against the invader. The forces they commanded were the first of the volunteer armies."</ref> After the 1936 [[Xi'an Incident]], the Kuomintang and communist forces agreed on a ceasefire to present [[Second United Front|a united front]] to oppose Japan.{{sfn|Busky|2002|p=10}}