Western Europe (1940–41)
In April 1940, Germany invaded Denmark and Norway to protect shipments of iron ore from Sweden, which the Allies were attempting to cut off by unilaterally mining neutral Norwegian waters. Denmark capitulated after a few hours, and despite Allied support, during which the important harbour of Narvik temporarily was recaptured by the British, Norway was conquered within two months. British discontent over the Norwegian campaign led to the replacement of the British Prime Minister, Neville Chamberlain, with Winston Churchill on 10 May 1940.
Germany launched an offensive against France and, for reasons of military strategy, also attacked the neutral nations of Belgium, the Netherlands, and Luxembourg on 10 May 1940. That same day the United Kingdom occupied the Danish possessions of Iceland, Greenland and the Faroes to preempt a possible German invasion of the islands. The Netherlands and Belgium were overrun using blitzkrieg tactics in a few days and weeks, respectively. The French-fortified Maginot Line and the main body the Allied forces which had moved into Belgium were circumvented by a flanking movement through the thickly wooded Ardennes region, mistakenly perceived by Allied planners as an impenetrable natural barrier against armoured vehicles. As a result, the bulk of the Allied armies found themselves trapped in an encirclement and were beaten.
Allied troops were forced to evacuate the continent at Dunkirk, abandoning their heavy equipment by early June. On 10 June, Italy invaded France, declaring war on both France and the United Kingdom; Paris fell on 14 June and eight days later France surrendered and was soon divided into German and Italian occupation zones, and an unoccupied rump state under the Vichy Regime, which, though officially neutral, was generally aligned with Germany. France kept its fleet but the British feared the Germans would seize it, so on 3 July, the British attacked it.
In June 1940, the Soviet Union forcibly annexed Estonia, Latvia and Lithuania, and then annexed the disputed Romanian region of Bessarabia. Meanwhile, Nazi-Soviet political rapprochement and economic co-operation gradually stalled, and both states began preparations for war.
On 19 July, Hitler again publicly offered to end the war, saying he had no desire to destroy the British Empire. The United Kingdom rejected this, with Lord Halifax responding "there was in his speech no suggestion that peace must be based on justice, no word of recognition that the other nations of Europe had any right to self‑determination "
Following this, Germany began an air superiority campaign over the United Kingdom (the Battle of Britain) to prepare for an invasion. The campaign failed, and the invasion plans were cancelled by September. Frustrated, and in part in response to repeated British air raids against Berlin, Germany began a strategic bombing offensive against British cities known as the Blitz. However, the air attacks largely failed to either disrupt the British war effort or convince them to sue for peace.
Using newly captured French ports, the German Navy enjoyed success against an over-extended Royal Navy, using U-boats against British shipping in the Atlantic. The British scored a significant victory on 27 May 1941 by sinking the German battleship Bismarck. Perhaps most importantly, during the Battle of Britain the Royal Air Force had successfully resisted the Luftwaffe's assault, and the German bombing campaign largely ended in May 1941.
Throughout this period, the neutral United States took measures to assist China and the Western Allies. In November 1939, the American Neutrality Act was amended to allow "cash and carry" purchases by the Allies. In 1940, following the German capture of Paris, the size of the United States Navy was significantly increased. In September, the United States further agreed to a trade of American destroyers for British bases. Still, a large majority of the American public continued to oppose any direct military intervention into the conflict well into 1941.
Although Roosevelt had promised to keep the United States out of the war, he nevertheless took concrete steps to prepare for that eventuality. In December 1940 he accused Hitler of planning world conquest and ruled out negotiations as useless, calling for the US to become an "arsenal for democracy" and promoted the passage of Lend-Lease aid to support the British war effort. In January 1941 secret high level staff talks with the British began for the purposes of determining how to defeat Germany should the US enter the war. They decided on a number of offensive policies, including an air offensive, the "early elimination" of Italy, raids, support of resistance groups, and the capture of positions to launch an offensive against Germany.
At the end of September 1940, the Tripartite Pact united Japan, Italy and Germany to formalise the Axis Powers. The Tripartite Pact stipulated that any country, with the exception of the Soviet Union, not in the war which attacked any Axis Power would be forced to go to war against all three. The Axis expanded in November 1940 when Hungary, Slovakia and Romania joined the Tripartite Pact. Romania would make a major contribution (as did Hungary) to the Axis war against the USSR, partially to recapture territory ceded to the USSR, partially to pursue its leader Ion Antonescu's desire to combat communism.
Italy began operations in the Mediterranean, initiating a siege of Malta in June, conquering British Somaliland in August, and making an incursion into British-held Egypt in September 1940. In October 1940, Italy started the Greco-Italian War due to Mussolini's jealousy of Hitler's success but within days was repulsed and pushed back into Albania, where a stalemate soon occurred. The United Kingdom responded to Greek requests for assistance by sending troops to Crete and providing air support to Greece. Hitler decided to take action against Greece when the weather improved to assist the Italians and prevent the British from gaining a foothold in the Balkans, to strike against the British naval dominance of the Mediterranean, and to secure his hold on Romanian oil.
In December 1940, British Commonwealth forces began counter-offensives against Italian forces in Egypt and Italian East Africa. The offensive in North Africa was highly successful and by early February 1941 Italy had lost control of eastern Libya and large numbers of Italian troops had been taken prisoner. The Italian Navy also suffered significant defeats, with the Royal Navy putting three Italian battleships out of commission by a carrier attack at Taranto, and neutralising several more warships at the Battle of Cape Matapan.
The Germans soon intervened to assist Italy. Hitler sent German forces to Libya in February, and by the end of March they had launched an offensive which drove back the Commonwealth forces who had been weakened to support Greece. In under a month, Commonwealth forces were pushed back into Egypt with the exception of the besieged port of Tobruk. The Commonwealth attempted to dislodge Axis forces in May and again in June, but failed on both occasions.
By late March 1941, following Bulgaria's signing of the Tripartite Pact, the Germans were in position to intervene in Greece. Plans were changed, however, due to developments in neighbouring Yugoslavia. The Yugoslav government had signed the Tripartite Pact on 25 March, only to be overthrown two days later by a British-encouraged coup. Hitler viewed the new regime as hostile and immediately decided to eliminate it. On 6 April Germany simultaneously invaded both Yugoslavia and Greece, making rapid progress and forcing both nations to surrender within the month. The British were driven from the Balkans after Germany conquered the Greek island of Crete by the end of May. Although the Axis victory was swift, bitter partisan warfare subsequently broke out against the Axis occupation of Yugoslavia, which continued until the end of the war.
The Allies did have some successes during this time. In the Middle East, Commonwealth forces first quashed an uprising in Iraq which had been supported by German aircraft from bases within Vichy-controlled Syria, then, with the assistance of the Free French, invaded Syria and Lebanon to prevent further such occurrences.
Axis attack on the USSR (1941)
With the situation in Europe and Asia relatively stable, Germany, Japan, and the Soviet Union made preparations. With the Soviets wary of mounting tensions with Germany and the Japanese planning to take advantage of the European War by seizing resource-rich European possessions in Southeast Asia, the two powers signed the Soviet–Japanese Neutrality Pact in April 1941. By contrast, the Germans were steadily making preparations for an attack on the Soviet Union, amassing forces on the Soviet border.
Hitler believed that Britain's refusal to end the war was based on the hope that the United States and the Soviet Union would enter the war against Germany sooner or later. He accordingly decided to try to strengthen Germany's relations with the Soviets, or failing that, to attack and eliminate them as a factor. In November 1940 negotiations took place to determine if the Soviet Union would join the Tripartite Pact. The Soviets showed some interest, but asked for concessions from Finland, Bulgaria, Turkey, and Japan that Germany considered unacceptable. On 18 December 1940 Hitler issued the directive to prepare for an invasion of the Soviet Union.
On 22 June 1941, Germany, Italy and Romania invaded the Soviet Union in Operation Barbarossa, with Germany accusing the Soviets of plotting against them. They were joined shortly by Finland and Hungary. The primary targets of this surprise offensive were the Baltic region, Moscow and Ukraine, with the ultimate goal of ending the 1941 campaign near the Arkhangelsk-Astrakhan line, from the Caspian to the White Seas. Hitler's objectives were to eliminate the Soviet Union as a military power, exterminate Communism, generate Lebensraum ("living space") by dispossessing the native population and guarantee access to the strategic resources needed to defeat Germany's remaining rivals.
Although the Red Army was preparing for strategic counter-offensives before the war, Barbarossa forced the Soviet supreme command to adopt a strategic defence. During the summer, the Axis made significant gains into Soviet territory, inflicting immense losses in both personnel and materiel. By the middle of August, however, the German Army High Command decided to suspend the offensive of a considerably depleted Army Group Centre, and to divert the 2nd Panzer Group to reinforce troops advancing towards central Ukraine and Leningrad. The Kiev offensive was overwhelmingly successful, resulting in encirclement and elimination of four Soviet armies, and made further advance into Crimea and industrially developed Eastern Ukraine (the First Battle of Kharkov) possible.
The diversion of three quarters of the Axis troops and the majority of their air forces from France and the central Mediterranean to the Eastern Front prompted Britain to reconsider its grand strategy. In July, the UK and the Soviet Union formed a military alliance against Germany The British and Soviets invaded Iran to secure the Persian Corridor and Iran's oil fields. In August, the United Kingdom and the United States jointly issued the Atlantic Charter.
By October, when Axis operational objectives in Ukraine and the Baltic region were achieved, with only the sieges of Leningrad and Sevastopol continuing, a major offensive against Moscow had been renewed. After two months of fierce battles, the German army almost reached the outer suburbs of Moscow, where the exhausted troops were forced to suspend their offensive. Large territorial gains were made by Axis forces, but their campaign had failed to achieve its main objectives: two key cities remained in Soviet hands, the Soviet capability to resist was not broken, and the Soviet Union retained a considerable part of its military potential. The blitzkrieg phase of the war in Europe had ended.
By early December, freshly mobilised reserves allowed the Soviets to achieve numerical parity with Axis troops. This, as well as intelligence data that established a minimal number of Soviet troops in the East sufficient to prevent any attack by the Japanese Kwantung Army, allowed the Soviets to begin a massive counter-offensive that started on 5 December all along the front and pushed German troops 100–250 kilometres (62–155 mi) west.