Invasion of Ethiopia

The Second Italo–Abyssinian War was a brief colonial war that began in October 1935 and ended in May 1936. The war was fought between the armed forces of the Kingdom of Italy (Regno d'Italia) and the armed forces of the Ethiopian Empire (also known as Abyssinia). The war resulted in the military occupation of Ethiopia and its annexation into the newly created colony of Italian East Africa (Africa Orientale Italiana, or AOI); in addition, it exposed the weakness of the League of Nations as a force to preserve peace. Both Italy and Ethiopia were member nations, but the League did nothing when the former clearly violated the League's own Article X.

Japanese invasion of China

In July 1937, Japan captured the former Chinese imperial capital of Beiping after instigating the Marco Polo Bridge Incident, which culminated in the Japanese campaign to invade all of China. The Soviets quickly signed a non-aggression pact with China to lend materiel support, effectively ending China's prior cooperation with Germany. Generalissimo Chiang Kai-shek deployed his best army to defend Shanghai, but after 3 months of fighting Shanghai fell. The Japanese continued to push the Chinese forces back, capturing the capital Nanjing in December 1937 and committed the Nanking Massacre.

In June 1938, Chinese forces stalled the Japanese advance by flooding the Yellow River; although this manoeuvre bought time for the Chinese to prepare their defences at Wuhan, the city was taken by October. However, Japanese military victories did not bring about the collapse of Chinese resistance that Japan had hoped to achieve, instead the Chinese government relocated inland to Chongqing to continue their resistance.

Japanese invasion of the USSR and Mongolia

On 29 July 1938, the Japanese invaded the USSR and were checked at the Battle of Lake Khasan. Although the battle was a Soviet victory, the Japanese dismissed it as an inconclusive draw, and on 11 May 1939 decided to move the Japanese-Mongolian border up to the Khalkin Gol River by force. After initial successes the Japanese assault on Mongolia was checked by the Red Army that inflicted the first major defeat on the Japanese Kwangtung Army.

These clashes convinced the Japanese government that they should focus on conciliating the Soviet government to avoid interference in the war against China and instead turn their military attention southward, towards the US and European holdings in the Pacific. They also prevented the sacking of experienced Soviet military leaders such as Zhukov, who would later play a vital role in the defence of Moscow.

European occupations and agreements

In Europe, Germany and Italy were becoming bolder. In March 1938, Germany annexed Austria, again provoking little response from other European powers. Encouraged, Hitler began pressing German claims on the Sudetenland, an area of Czechoslovakia with a predominantly ethnic German population; and soon France and Britain conceded this territory to him, against the wishes of the Czechoslovak government, in exchange for a promise of no further territorial demands. Soon after that, however, Germany and Italy forced Czechoslovakia to cede additional territory to Hungary and Poland. In March 1939, Germany invaded the remainder of Czechoslovakia and subsequently split it into the German Protectorate of Bohemia and Moravia and the pro-German client state, the Slovak Republic.

Alarmed, and with Hitler making further demands on Danzig, France and Britain guaranteed their support for Polish independence; when Italy conquered Albania in April 1939, the same guarantee was extended to Romania and Greece. Shortly after the Franco-British pledge to Poland, Germany and Italy formalised their own alliance with the Pact of Steel.

In August 1939, Germany and the Soviet Union signed the Molotov–Ribbentrop Pact, a non-aggression treaty with a secret protocol. The parties gave each other rights, “in the event of a territorial and political rearrangement,” to “spheres of influence” (western Poland and Lithuania for Germany, and eastern Poland, Finland, Estonia, Latvia and Bessarabia for the USSR). It also raised the question of continuing Polish independence.

World War I radically altered the diplomatic and political situations in Eurasia and Africa with the defeat of the Central Powers, including Austria-Hungary, Germany, and the Ottoman Empire; and the 1917 Bolshevik seizure of power in Russia. Meanwhile the success of the Allied Entente powers including the United Kingdom, France, the United States, Italy, Serbia, and Romania and the creation of new states from the collapse of Austria-Hungary and the Russian Empire resulted in a major shift in the balance of power from central and eastern Europe to the Atlantic littoral. In the aftermath of the war major unrest in Europe rose, especially irredentist and revanchist nationalism and class conflict. Irredentism and revanchism were strong in Germany because she was forced to accept significant territorial, colonial, and financial losses as part of the Treaty of Versailles. Under the treaty Germany lost around 13 percent of its home territory and all of its overseas colonies, while German annexation of other states was prohibited, massive reparations were imposed and limits were placed on the size and capability of Germany's armed forces. Meanwhile, the Russian Civil War had led to the creation of the Soviet Union. After Lenin's death in 1924, Stalin seized power in the USSR and repudiated the New Economic Policy favouring the Five Year Plans instead.

In the interwar period, domestic civil conflict occurred in Germany involving nationalists and reactionaries versus communists and moderate democratic political parties. A similar scenario occurred in Italy. Although Italy as an Entente ally made some territorial gains, Italian nationalists were angered that the terms of the Treaty of London upon which Italy had agreed to wage war on the Central Powers, were not fulfilled with the peace settlement. From 1922 to 1925, the Italian Fascist movement led by Benito Mussolini seized power in Italy with a nationalist, totalitarian, and class collaborationist agenda that abolished representative democracy, repressed political forces supporting class conflict or liberalism, and pursued an aggressive foreign policy aimed at forcefully forging Italy as a world power, and promising to create a "New Roman Empire." In Germany, the Nazi Party led by Adolf Hitler pursued establishing such a fascist government in Germany. With the onset of the Great Depression, Nazi support rose and, in 1933, Hitler was appointed Chancellor of Germany, and in the aftermath of the Reichstag fire, Hitler created a totalitarian single-party state led by the Nazis.

The Kuomintang (KMT) party in China launched a unification campaign against regional warlords and nominally unified China in the mid-1920s, but was soon embroiled in a civil war against its former Chinese communist allies. In 1931, an increasingly militaristic Japanese Empire, which had long sought influence in China as the first step of its right to rule Asia, used the Mukden Incident as justification to invade Manchuria and established the puppet state of Manchukuo. Too weak to resist Japan, China appealed to the League of Nations for help. Japan withdrew from the League of Nations after being condemned for its incursion into Manchuria. The two nations then fought several minor conflicts, in Shanghai, Rehe and Hebei, until signing the Tanggu Truce in 1933. Thereafter, Chinese volunteer forces continued the resistance to Japanese aggression in Manchuria, and Chahar and Suiyuan.

Adolf Hitler, after an unsuccessful attempt to overthrow the German government in 1923, became the Chancellor of Germany in 1933. He abolished democracy, espousing a radical, racially motivated revision of the world order, and soon began a massive rearmament campaign. Meanwhile, France, to secure its alliance, allowed Italy a free hand in Ethiopia, which Italy desired as a colonial possession. The situation was aggravated in early 1935 when the Saarland was legally reunited with Germany and Hitler repudiated the Treaty of Versailles, speeding up his rearmament programme and introducing conscription.

Hoping to contain Germany, the United Kingdom, France and Italy formed the Stresa Front. The Soviet Union, concerned due to Germany's goals of capturing vast areas of eastern Europe, wrote a treaty of mutual assistance with France. Before taking effect though, the Franco-Soviet pact was required to go through the bureaucracy of the League of Nations, which rendered it essentially toothless. However, in June 1935, the United Kingdom made an independent naval agreement with Germany, easing prior restrictions. The United States, concerned with events in Europe and Asia, passed the Neutrality Act in August. In October, Italy invaded Ethiopia, with Germany the only major European nation supporting the invasion. Italy then revoked objections to Germany's goal of absorbing Austria.

Hitler defied the Versailles and Locarno treaties by remilitarizing the Rhineland in March 1936. He received little response from other European powers. When the Spanish Civil War broke out in July, Hitler and Mussolini supported fascist Generalissimo Francisco Franco's nationalist forces in his civil war against the Soviet-supported Spanish Republic. Both sides used the conflict to test new weapons and methods of warfare, and the nationalists won the war in early 1939. Mounting tensions led to several efforts to strengthen or consolidate power. In October 1936, Germany and Italy formed the Rome-Berlin Axis. A month later, Germany and Japan signed the Anti-Comintern Pact, which Italy would join in the following year. In China, after the Xian Incident the Kuomintang and communist forces agreed on a ceasefire in order to present a united front to oppose Japan.

The start of the war is generally held to be 1 September 1939 beginning with the German invasion of Poland; Britain and France declared war on Germany two days later. Other dates for the beginning of war include the Japanese invasion of Manchuria on 13 September 1931; the start of the Second Sino-Japanese War on 7 July 1937; or one of several other events.

Others follow A. J. P. Taylor, who held that there was a simultaneous Sino-Japanese War in East Asia, and a Second European War in Europe and her colonies. The two wars merged in 1941, becoming a single global conflict, at which point the war continued until 1945. This article uses the conventional dating.

The exact date of the war's end is not universally agreed upon. It has been suggested that the war ended at the armistice of 14 August 1945 (V-J Day), rather than the formal surrender of Japan (2 September 1945); in some European histories, it ended on V-E Day (8 May 1945). The Treaty of Peace with Japan was not signed until 1951.

World War II, or the Second World War (often abbreviated as WWII or WW2), was a global military conflict lasting from 1939 to 1945 which involved most of the world's nations, including all of the great powers, organised into two opposing military alliances: the Allies and the Axis. It was the most widespread war in history, with more than 100 million military personnel mobilised. In a state of "total war", the major participants placed their entire economic, industrial, and scientific capabilities at the service of the war effort, erasing the distinction between civilian and military resources. Marked by significant action against civilians, including the Holocaust and the only use of nuclear weapons in warfare, it was the deadliest conflict in human history. Estimates range from fifty million to over seventy million fatalities. The war ended with the total victory of the Allies over Germany and Japan in 1945.

The war was fought between the Allies -- the United States, the United Kingdom, British Commonwealth forces and the Soviet Union -- against the Axis powers: Germany, Italy and Japan. The Allies were supported militarily by communist-led resistance movements throughout Europe and the Far East. British wartime leader Winston Churchill, in his voluminous history of World War II, depicts a generally cordial relationship between the Western allies and their Soviet allay. Documents declassified after the war provide a different perspective. In secret wartime correspondence between Soviet leader Josef Stalin and Churchill, Stalin complained repeatedly that by land, sea and air, the Western allies were failing to use their military forces to good effect while, as a result, the Soviet Union suffered appalling losses on the eastern or Russian-German front. Russian historians contend that the Eastern Front was the principal and decisive front of the war. Revisionist historians propose that, because of the wartime tensions that existed between Stalin and the Western leaders, the roots of the Cold War can be traced to events in World War II.

The end of World War II brought profound changes in international relations and political alliances. The League of Nations was replaced by the United Nationswith the intention of fostering international cooperation and prevent future conflicts. The Bretton Woods Agreement was signed to reform international financial institutions, and tariffs and trade, which were identified as having been among the main economic factors that had led to World War II. The Soviet Union and the United States emerged as rival superpowers in a nuclear arms race, while Western Europe began moving toward economic recovery and political integration.