Pre War Events
Italian invasion of Ethiopia (1935)
The Second Italo–Abyssinian War was a brief colonial war that began in October 1935 and ended in May 1936. The war began with the invasion of the Ethiopian Empire (also known as Abyssinia) my the armed forces of the Kingdom of Italy (Regno d'Italia), which was launched from Italian Somaliland and Eritrea. 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.
Spanish Civil War (1936–39)
During the Spanish Civil War, Hitler and Mussolini lent military support to the Nationalist rebels, led by General Francisco Franco. The Soviet Union supported the existing government, the Spanish Republic. Over 30,000 foreign volunteers, known as the International Brigades, also fought against the Nationalists. Both Germany and the USSR used this proxy war as an opportunity to test in combat their most advanced weapons and tactics. The bombing of Guernica by the German Condor Legion in April 1937 heightened widespread concerns that the next major war would include extensive terror bombing attacks on civilians. The Nationalists won the civil war in April 1939; Franco, now dictator, bargained with both sides during the Second World War, but never concluded any major agreements. He did send volunteers to fight on the eastern front under German command but Spain remained neutral and did not allow either side to use its territory.
Japanese invasion of China (1937)
In July 1937, Japan captured the former Chinese imperial capital of Beijing 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 co-operation with Germany. Generalissimo Chiang Kai-shek deployed his best army to defend Shanghai, but, after three months of fighting, Shanghai fell. The Japanese continued to push the Chinese forces back, capturing the capital Nanking in December 1937. After the fall of Nanking, tens of thousands if not hundreds of thousands of Chinese civilians and disarmed combatants were murdered by the Japanese.
In March 1938, Nationalist Chinese force got their first major victory at Taierzhuang but then city Xuzhou was taken by Japanese in May. In June 1938, Chinese forces stalled the Japanese advance by flooding the Yellow River; this manoeuvre bought time for the Chinese to prepare their defences at Wuhan, but the city was taken by October. 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 and continued the war.
Japanese invasion of the Soviet Union and Mongolia (1938)
These clashes convinced some factions in 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, and also prevented the sacking of experienced Soviet military leaders such as Georgy Zhukov, who would later play a vital role in the defense 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 Britain and France followed the counsel of prime minister Neville Chamberlain and conceded this territory to Germany in the Munich Agreement, which was made against the wishes of the Czechoslovak government, in exchange for a promise of no further territorial demands. Soon afterwards, Germany and Italy forced Czechoslovakia to cede additional territory to Hungary and Poland.
Although all of Germany's stated demands had been satisfied by the agreement, privately Hitler was furious that British interference had prevented him from seizing all of Czechoslovakia in one operation. In subsequent speeches Hitler attacked British and Jewish "war-mongers" and in January 1939 secretly ordered a major build-up of the German navy to challenge British naval supremacy. In March 1939, Germany invaded the remainder of Czechoslovakia and subsequently split it into the German Protectorate of Bohemia and Moravia and a pro-German client state, the Slovak Republic. Hitler also delivered an ultimatum to Lithuania, forcing the concession of the Klaipėda Region.
Alarmed, and with Hitler making further demands on the Free City of 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. Hitler accused Britain and Poland of trying to "encircle" Germany and renounced the Anglo-German Naval Agreement and the German–Polish Non-Aggression Pact.
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 to "spheres of influence" (western Poland and Lithuania for Germany; eastern Poland, Finland, Estonia, Latvia and Bessarabia for the USSR). It also raised the question of continuing Polish independence. The agreement was crucial to Hitler because it assured that Germany would not have to face the prospect of a two-front war, as it had in World War I, after it defeated Poland.
The situation reached a general crisis in late August as German troops continued to mobilise against the Polish border. In a private meeting with the Italian foreign minister, Count Ciano, Hitler asserted that Poland was a "doubtful neutral" that needed to either yield to his demands or be "liquidated" to prevent it from drawing off German troops in the future "unavoidable" war with the Western democracies. He did not believe Britain or France would intervene in the conflict. On 23 August Hitler ordered the attack to proceed on 26 August, but upon hearing that Britain had concluded a formal mutual assistance pact with Poland and that Italy would maintain neutrality, he decided to delay it. In response to British pleas for direct negotiations, Germany demanded on 29 August that a Polish plenipotentiary immediately travel to Berlin to negotiate the handover of Danzig and the Polish Corridor to Germany as well as to agree to safeguard the German minority in Poland. The Poles refused to comply with this request and on the evening of 31 August Germany declared that it considered its proposals rejected.
Course of the war
War breaks out in Europe (1939–40)
On 1 September 1939, Germany invaded Poland, on the false pretext that Poland had launched attacks on German territory. On 3 September France and United Kingdom; followed by the fully independent Dominions of the British Commonwealth, – Australia, Canada, New Zealand and South Africa – declared war on Germany. But, provided limited direct support to Poland other than a small French attack into the Saarland. United Kingdom and France also began a naval blockade of Germany on 3 September which aimed to damage the country's economy and war effort. Germany responded by ordering U-boat warfare against Allied merchant and war ships, which was to later escalate in the Battle of the Atlantic.
On 17 September 1939, after signing a cease-fire with Japan, the Soviets also invaded Poland from the east. The Polish army was defeated and Warsaw surrendered to the Germans on 27 September, with final pockets of resistance surrendering on 6 October. Poland's territory was divided between Germany and the Soviet Union, with Lithuania and Slovakia also receiving small shares. The Poles did not fully surrender; they established a Polish Underground State, an underground Home Army, and continued to fight alongside the Allies on all fronts in Europe and North Africa.
About 100,000 Polish military personnel were evacuated to Romania and the Baltic countries; many of these soldiers later fought against the Germans in other theatres of the war. Poland's Enigma codebreakers were also evacuated to France.
On 6 October Hitler made a public peace overture to the United Kingdom and France, but said that the future of Poland was to be determined exclusively by Germany and the Soviet Union. Chamberlain rejected this on 12 October, saying "Past experience has shown that no reliance can be placed upon the promises of the present German Government." After this rejection Hitler ordered an immediate offensive against France, but his generals persuaded him to wait until May of next year.
After signing the German-Soviet treaty governing Lithuania, the Soviet Union forced the Baltic countries to allow it to station Soviet troops in their countries under pacts of "mutual assistance." Finland rejected territorial demands and was invaded by the Soviet Union in November 1939. The resulting Winter War ended in March 1940 with Finnish concessions. The United Kingdom and France treating the Soviet attack on Finland as tantamount to its entering the war on the side of the Germans, responded to the Soviet invasion by supporting the USSR's expulsion from the League of Nations.
In December 1939 the United Kingdom won a naval victory over Germany in the south Atlantic during the Battle of the River Plate.