In June 1940 the Soviet Union occupied Latvia, Lithuania, and Estonia, and annexed Bessarabia and Northern Bukovina from Romania. Not having secured a rapid peace with the United Kingdom, Germany began preparations to invade with the Battle of Britain. Fighter aircraft fought overhead for months as the Luftwaffe and Royal Air Force fought for control of Britain's skies. The Luftwaffe initially targeted RAF Fighter Command but turned to terror bombing London. The Luftwaffe was not successful, and Operation Sealion, the proposed invasion of the British Isles, was abandoned. Similar efforts were made, though at sea, in the Battle of the Atlantic. In a long-running campaign, German U-Boats attempted to deprive the British Isles of necessary Lend Lease cargo from the United States. The U-Boats reduced shipments considerably; however, the United Kingdom refused to seek peace, with Prime Minister Winston Churchill stating that "We shall never surrender". President Roosevelt announced a shift in the American stance from neutrality to "non-belligerency".

The Mediterranean: Italy invaded Greece on 28 October 1940, from bases in Albania. Greek forces successfully repelled the Italian attacks and launched a full-scale counter-attack deep into Albania. By mid-December they had occupied one-fourth of Albania. The North African Campaign began in 1940; Italian forces in Libya attacked British forces in Egypt. The aim was to make Egypt an Italian possession, especially the vital Suez Canal. British, Indian and Australian forces counter-attacked (see Operation Compass), but this offensive stopped in 1941 when much of the Commonwealth forces were transferred to Greece to defend it from German attack. However, German forces (known later as the Afrika Korps) under General Erwin Rommel landed in Libya and renewed the assault on Egypt. Italian troops invaded and captured British Somaliland in August 1940.

On the other hand, the Italian declaration of war challenged the British supremacy of this sea, a supremacy hinged on Gibraltar, Malta and Alexandria. While Gibraltar was never under direct attack, Alexandria and to a deadlier degree Malta were hit repeatedly by Axis attacks: the thrusts towards the Suez Canal for the former, and the 1940/42 Blitz for the latter, making the island of Malta the most heavily bombed place on earth.

Asia: In 1940, Japan occupied French Indochina (Vietnam) upon agreement with the Vichy Government and allied with the Axis powers, Germany and Italy. These actions intensified Japan's conflict with the United States and the United Kingdom, who reacted with an oil boycott.

World War II - 1941: The war becomes global

Main articles: Eastern Front (World War II), Continuation War, and Attack on Pearl Harbor

Europe: ^[6]Yugoslavia's government succumbed to the pressure of Italy and Germany and signed the Tripartite Treaty on 25 March 1941. This was followed by anti-Axis demonstrations in the country and a coup which overthrew the government and replaced it with a pro-Allied one on 27 March 1941. Hitler's forces then invaded Greece and Yugoslavia on 6 April 1941. Hitler reluctantly sent forces to assist Mussolini's forces in their attempt to capture Greece, principally to prevent a British build-up on Germany's strategic southern flank. With these new troops the Axis succeeded in driving the Greek forces back. British troops were diverted from North Africa to assist with the defence but failed to prevent Greece's capture. On 20 May 1941, the Battle of Crete began when elite German Fallschirmjäger and glider-borne mountain troops and some 539 aeroplanes launched a massive airborne invasion of the Greek island of Crete. Crete was defended by an group of about 43,000 Greek, New Zealand, Australian and British troops, not all of them fully equipped. The Germans attacked the island simultaneously on the three airfields. Their invasion on two of the airfields failed, but they successfully captured one, which allowed them to reinforce their position by landing reinforcements. After a week it was decided that so many German troops had been flown in that there was no way to defeat them, and about 17,000 Commonwealth soldiers were evacuated. However, over 10,000 Greek and 500 Commonwealth troops remained at large and caused problems for the German occupiers. The German invasion troops suffered 6,200 casualties (with almost 4,000 dead) out of 14,000 used. So heavy were the losses that Hitler decided never to launch an airborne invasion again. General Kurt Student would later say, "Crete was the grave of the German parachutists". The Allies, on the other hand, came to the conclusion that every major invasion should be supported by paratroopers.

Operation Barbarossa, the German invasion of the Soviet Union, the largest invasion in history, commenced on 22 June 1941. The "Great Patriotic War" (Russian: Великая Отечественная Война, Velikaya Otechestvennaya Voyna) had begun with surprise attacks by German panzer armies, which encircled and destroyed much of the Soviet's western military, capturing or killing hundreds of thousands of men. Soviet forces came to fight a war of scorched earth, withdrawing into the steppe of Russia to acquire time and stretch the German army. Industries were dismantled and withdrawn to the Ural mountains for reassembly. German armies pursued a three-pronged advance against Leningrad, Moscow, and the Caucasus. Having pushed to occupy Moscow before winter, German forces were delayed into the Soviet Winter. Soviet counter-attacks defeated them within sight of Moscow's spires, and a rout was only narrowly avoided. Some historians identify this as the "turning point" in the Allies' war against Germany; others identify the capitulation of the German Sixth Army outside Stalingrad (modern-day Volgograd) in 1943. The Continuation War between Finland and the Soviet Union began with Soviet air attacks shortly after the beginning of Operation Barbarossa, on 25 June, and ended with an armistice in 1944.

The Mediterranean: In June 1941, Allied forces invaded Syria and Lebanon, capturing Damascus on 17 June (see Syria-Lebanon campaign). Meanwhile, Rommel's forces advanced rapidly eastward, laying siege to the vital seaport of Tobruk. Australian and other Allied troops in the city resisted all until relieved, but a renewed Axis offensive captured the city and drove the Eighth Army back to a line at El Alamein.

Asia: The Sino-Japanese War

A war had begun in Asia years before World War II started in Europe. Japan had invaded China in 1931. By 1937, war had broken out as the Japanese sought control of China. Roosevelt signed an unpublished (secret) executive order in May 1940 allowing U.S. military personnel to resign from the service so that they could participate in a covert operation in China: the American Volunteer Group, also known as Chennault's Flying Tigers. Over a seven-month period, Chennault's Flying Tigers destroyed an estimated 115 Japanese aircraft, sunk numerous Japanese ships, and had a notable participation in the campaign of Burma. With the United States and other countries cutting exports to Japan, particularly fuel oil, Japan planned a strike on Pearl Harbor on Sunday, 7 December 1941, to cripple the U.S. Pacific Fleet while consolidating oil fields in Southeast Asia. It is hard to determine whether the Japanese intended to release an advance declaration of war, however, as means of coordinating secret directives with public communication, particularly during a weekend in the U.S., were limited. Despite what warning signs remained, the attack on Pearl Harbor achieved military surprise and dealt severe damage to the American Fleet's battleships, though the primary targets, aircraft carriers, remained safely at sea.

On December 8, 1941 Japanese forces arrived at Hong Kong, which later led to the Battle of Hong Kong. With a combined force of only 14,000, the Canadian Army, British Army and the British Indian Army, the vastly outnumbered Allied troops held out until the surrender of the British colony on Christmas Day (known to locals as 'Black Christmas').

Asia: The United States enters the war

On 7 December 1941, Japanese warplanes commanded by Vice Admiral Chuichi Nagumo carried out a surprise air raid on Pearl Harbor, Hawaii, the largest U.S. naval base in the Pacific. The Japanese forces met little resistance and devastated the harbor. This attack resulted in 8 battleships ( including the California, the Utah, the West Virginia, the Oklahoma, the Arizona,and the Tennesee) either sunk or damaged, 3 light cruisers and 3 destroyers sunk as well as damage to some auxiliaries and 343 aircraft either damaged or destroyed. 2408 Americans were killed including 68 civilians; 1178 were wounded. Japan lost only 29 aircraft and their crews and five midget submarines. However, the attack failed to strike targets that could have been crippling losses to the US Pacific Fleet such as the aircraft carriers which were out at sea at the time of the attack or the base's ship fuel storage and repair facilities. The survival of these assets have led many to consider this attack a catastrophic long term strategic blunder for Japan.

The following day, the United States declared war on Japan. The same day, China officially declared war on Japan despite having been engaged in warfare for over four years (it had done so in order to receive military aid as to avoid neutrality complications). Simultaneous to the attack on Pearl Harbor, Japan also attacked U.S. air bases in the Philippines. Immediately following these attacks, Japan invaded the Philippines and also the British Colonies of Hong Kong, Malaya, Borneo and Burma with the intention of seizing the oilfields of the Dutch East Indies. In a matter of months, all these territories and more fell to the Japanese. The British island fortress of Singapore was captured in what Churchill considered one of the most humiliating British defeats of all time.

Following the Japanese attack on Pearl Harbor, Germany declared war on the United States on 11 December 1941, even though it was not obliged to do so under the Tripartite Pact of 1940. Hitler made the declaration in the hopes that Japan would support him by attacking the Soviet Union. Japan did not oblige him, and this diplomatic move proved a catastrophic blunder which gave President Franklin D. Roosevelt the pretext needed for the United States joining the fight in Europe with full commitment and with no meaningful opposition from Congress. Some historians mark this moment as another major turning point of the war with Hitler provoking a grand alliance of powerful nations, most prominently the UK, the USA and the USSR, who could wage powerful offensives on both East and West simultaneously.

World War II - 1942: Deadlock

Main articles: Battle of Stalingrad, Operation Torch

In May 1942, one of the most powerful Nazis, Reinhard Heydrich, was assassinated in Prague in the Operation Anthropoid. In the Eastern front, an aborted German offensive was launched towards the Caucasus to secure oil fields, and German armies reached Stalingrad. The siege of Stalingrad continued for many months, with vicious urban warfare leading to high casualties on both sides. At night, the Soviet forces were resupplied from the east bank of the Volga, and the Wehrmacht forces were eventually ground down; especially after Hitler diverted the armor of the Sixth Army to the Caucasus. In November a Soviet offensive encircled the Sixth Army. By early February 1943, it was clear that the Sixth Army would have to surrender. Hitler promoted General Friedrich Paulus, who was in charge of the German forces in the area, to Field Marshal in the vain hope it would deter him from surrendering because never before has a German Field Marshall had ever surrendered. It did not, and he surrendered completely on 2 February. The results were the destruction of the city, millions of casualties, and the collapse of Wehrmacht's Sixth Army as a viable fighting force. Nazi Propaganda Minister Joseph Goebbels responded with his Sportpalast speech to the German people. Some historians cite this as the European war's "turning point".

The First Battle of El Alamein took place between 1 July and 27 July 1942. German forces had advanced to the last defensible point before Alexandria and the Suez Canal. However, they had outrun their supplies, and a Commonwealth defence stopped their thrusts. The Second Battle of El Alamein occurred between October 23 and November 3, 1942, after Field Marshal Bernard Montgomery had replaced Claude Auchinleck as commander of the Commonwealth forces, now known as the Eighth Army. Erwin Rommel, German commander of the Afrika Korps, known as the "Desert Fox", was absent from the battle because he was recovering from jaundice back in Europe. Commonwealth forces took the offensive, and although they lost more tanks than the Germans began the battle with, Montgomery was ultimately triumphant. The western Allies had the advantage of being close to their supplies during the battle. In addition, Rommel was getting little or no help by this time from the struggling Luftwaffe, which was now more tasked with defending Western European air space, and fighting the Soviet Union, than providing Rommel with support in North Africa. After the German defeat at El Alamein, Rommel made a successful strategic withdrawal to Tunisia. During the Arcadia Conference from December 1941 to January 1942, the Allied leaders concluded that it was essential to keep Russia in the war. This consideration led to the overall strategy "Germany First"; i.e. giving priority of knocking out Germany before Japan. This decision resulted in a long debate as to where and when to open a Second Front against Germany. The American Chiefs of Staff favored a cross-channel (France) amphibious operation in the summer. The British opposed this because of insufficient landing craft and logistical problems. It was also thought that American forces were in a process of expansion, organization and exercise, not capable yet of fighting an experienced German army. Only if Russia collapsed would they approve a main landing in France. Churchill put forward the idea of a small invasion in Norway or landings in French North Africa. The plan for landings in Africa was approved in July 1942.

Operation Torch was headed by General Dwight Eisenhower. The aim of Torch was to gain control of Morocco and Algiers through simultaneous landings at Casablanca, Oran and Algiers, followed a few days later with a landing at Bône, the gateway to Tunisia. The operation was launched on 8 November 1942. The first wave was almost entirely American troops, because it was thought that the French would react more favorably to Americans than British. It was hoped that the local forces of Vichy France would put up no resistance and submit to the authority of Free French General Henri Giraud. In fact, resistance was stronger than expected but still sporadic. In Algiers, 400 members of the French resistance captured much of the city, though it was retaken before Allied forces could arrive. The Vichy commander, Admiral Darlan, negotiated an end to hostilities, against orders from the Vichy government. He was allowed to retain local control by the Allies, to the annoyance of Free French leaders. Hitler invaded and occupied Vichy France in response. Rommel's Afrika Corps was not being supplied adequately because of the loss of transport shipments caused by Allied—mostly British—navies and air forces in the Mediterranean. This lack of supplies and air support destroyed any chance of a large German offensive in Africa. Ultimately, German and Italian forces were caught in the pincers of a twin advance from Algeria and Libya. The withdrawing Germans continued to put up stiff defence, and Rommel defeated the American forces decisively at the Battle of Kasserine Pass before finishing his strategic withdrawal back to the meagre German supply chain. Inevitably, advancing from both the east and west, the Allies finally defeated the German Afrika Corps on May 13, 1943. Some 250,000 Axis soldiers were taken prisoner.

A substantial element of the Asian campaign was played out, starting in 1942, in the Aleutian Islands. On August 7, 1943, a combined American-Canadian force invaded the Aleutian Island only to find them abandoned.

World War II - 1943: The war turns

Main articles: Battle of Kursk, Italian Campaign (World War II), and Italian Campaign

Russia: After the victory at Stalingrad, the Red Army launched eight offensives during the winter, many concentrated along the Don basin near Stalingrad, which resulted in initial gains until German forces were able to take advantage of the weakened condition of the Red Army and regain the territory it lost. In July, the Wehrmacht launched a much-delayed offensive against the Soviet Union at Kursk. Their intentions were known by the Soviets, and the Battle of Kursk ended in a Soviet counteroffensive that threw the German Army back.

Italy: Newly captured North Africa was used as a springboard for the invasion of Sicily on 10 July 1943. On 25 July Benito Mussolini was fired from office by the King of Italy, allowing a new government to take power. Having captured Sicily, the Allies invaded mainland Italy on 3 September 1943. Italy surrendered on 8 September, but German forces continued to fight. Allied forces advanced north but were stalled for the winter at the Gustav Line, until they broke through in the Battle of Monte Cassino. Rome was captured on 5 June 1944. Mid-1943 brought the fifth and final German Sutjeska offensive against the Yugoslav Partisans before the invasion and subsequent capitulation of Italy, the other major occupying force in Yugoslavia.

Asia: (1943–45): Australian and U.S. forces then undertook the prolonged campaign to retake the occupied parts of the Solomon Islands, New Guinea and the Dutch East Indies, experiencing some of the toughest resistance of the war. The rest of the Solomon Islands were retaken in 1943, New Britain and New Ireland in 1944. As the Philippines were being retaken in late 1944, the Battle of Leyte Gulf raged, arguably the largest naval battle in history. The last major offensive in the south-west Pacific Area was the Borneo campaign of mid-1945, which was aimed at further isolating the remaining Japanese forces in South East Asia and securing the release of Allied POWs. Allied submarines and aircraft also attacked Japanese merchant shipping, depriving Japan's industry of the raw materials it had gone to war to obtain. The effectiveness of this stranglehold increased as U.S. Marines captured islands closer to the Japanese mainland. The Nationalist Kuomintang Army, under Chiang Kai-shek, and the Communist Chinese Army, under Mao Zedong, both opposed the Japanese occupation of China but never truly allied against the Japanese. Conflict between Nationalist and Communist forces emerged long before the war; it continued after and, to an extent, even during the war, though more implicitly. The Japanese had captured most of Burma, severing the Burma Road by which the Western Allies had been supplying the Chinese Nationalists. This forced the Allies to create a large sustained airlift, known as "flying the Hump". U.S. led and trained Chinese divisions, a British division and a few thousand U.S. ground troops cleared the Japanese forces from northern Burma so that the Ledo Road could be built to replace the Burma Road. Further south the main Japanese army in the theatre were fought to a standstill on the Burma-India frontier by the British Fourteenth Army (the "Forgotten Army"), which then counter-attacked, and having recaptured all of Burma was planning attacks towards Malaya when the war ended.

World War II - 1944: The beginning of the end

Main articles: Battle of Normandy, Operation Bagration, Operation Market Garden, and Battle of the Bulge

^[7]On "D-Day" (6 June 1944) the western Allies invaded German-held Normandy in a pre-dawn amphibious assault spearheaded by American (82nd and 101st), British (6th) and Canadian paratroopers, opening the "second front" against Germany. The allies suffered large casualties during the beach assault. German artillery batteries pounded the beaches. But the airborne divisions secured the rear, enabling the seaborne troops to break inland. ² Hedgerows aided the defending German units by giving them perfect areas for MG 42 emplacemtents. The narrow causeways of the hedgerow lanes caused great difficulty for tankers and eliminated their ability to rotate it's turret. Troops also refered to the causeways as death-alleys because the Germans had the entire length zeroed in with mortars and 88's. The hedgerows themselves proved impossible to penetrate and if a Sherman attempted to run-over these walls they exposed their vulnerable underbellies to panzerfaust fire. For months the Allies measured progress in hundreds of yards and bloody rifle fights in the Bocage. An Allied breakout was effected at St.-Lô, and the most powerful German force in France, the Seventh Army, was almost completely destroyed in the Falaise pocket while counter-attacking. Allied forces stationed in Italy invaded the French Riviera on 15 August and linked up with forces from Normandy. The clandestine French Resistance in Paris rose against the Germans on 19 August, and a French division under General Jacques Leclerc, pressing forward from Normandy, received the surrender of the German forces there and liberated the city on August 25. By early 1944, the Red Army had reached the border of Poland and lifted the Siege of Leningrad.

Shortly after Allied landings at Normandy, on 9 June, the Soviet Union began an offensive on the Karelian Isthmus that after three months would force Nazi Germany's co-belligerent Finland to an armistice. Operation Bagration, a Soviet offensive involving 2.5 million men and 6,000 tanks, was launched on 22 June, destroying the German Army Group Centre and taking 350,000 prisoners. Finland's defence had been dependent on active, or in periods passive, support from the German Wehrmacht that also provided defence for the chiefly uninhabited northern half of Finland. After the Wehrmacht retreated from the southern shores of the Gulf of Finland, Finland's defence was untenable. The Allies' armistice conditions included further territorial losses and the internment or expulsion of German troops on Finnish soil executed in the Lapland War, now as co-belligerents of the Allies, who also demanded the political leadership to be prosecuted in "war-responsibility trials", which the Finnish public perceived as a mockery of the rule of law.

Allied paratroopers attempted a fast advance into Germany with Operation Market Garden in September but were repulsed. Logistical problems were starting to plague the Allies' advance west as the supply lines still ran back to the beaches of Normandy. A decisive victory by the Canadian First Army in the Battle of the Scheldt secured the entrance to the port of Antwerp, freeing it to receive supplies by late November 1944. Romania surrendered in August 1944 and Bulgaria in September. The Warsaw Uprising was fought between 1 August and 2 October. Germany withdrew from the Balkans and held Hungary until February 1945.

In December 1944, the German Army made its last major offensive in the West, largely because even if successful in the east it would have had no effect on the massive Red Army rolling towards the Reich. Thus, Hitler thought he could drive a wedge between the frequently feuding Western Allies, causing them to agree to a favorable armistice, after which Germany could concentrate all her efforts on the Eastern front and have a chance to defeat the Soviets. The mission was unrealistic to begin with, since German plans largely relied on capturing Allied fuel dumps in order to keep their vehicles moving with the goal of capturing the vital port of Antwerp, and thus crippling the Allies in the Battle of the Bulge. At first, the Germans scored successes against the Americans stationed in the Ardennes. The Allied forces, largely unprepared for this sudden attack, suffered heavy casualties. In addition, the weather during the initial days of the invasion favored the Germans because the bad weather grounded Allied aircraft. However, with the overcast skies clearing allowing Allied air supremacy to enter the equation, and with the German failure to capture Bastogne, as well as the arrival of General Patton's Third Army, the Germans were forced to retreat back into Germany. The offensive was defeated. By now, the Soviets had reached the eastern borders of pre-war Germany.

By this time the Soviet steamroller had become so powerful that some historians argue that the U.S., British and Canadian landing at Normandy was more to prevent a coast-to-coast Soviet block than to fight Germany. On the other hand, some say that throughout the war Stalin called on the U.S. to open up a second front. Throughout the war, the Soviet Union engaged roughly 80%^{[citation needed]} of all Germany's forces.

The bombing of Dresden by the British Royal Air Force (RAF) and the United States Army Air Force (USAAF) between February 13 and February 15, 1945 remains one of the more controversial events of World War II.

According to British historian Frederick Taylor:

"The destruction of Dresden has an epically tragic quality to it. It was a wonderfully beautiful city and a symbol of baroque humanism and all that was best in Germany. It also contained all of the worst from Germany during the Nazi period. In that sense it is an absolutely exemplary tragedy for the horrors of 20th Century warfare..."[1]

World War II - 1945: The end of the war

Main articles: Borneo campaign (1945), End of World War II in Europe, Atomic bombings of Hiroshima and Nagasaki, and Victory over Japan Day

Churchill, Stalin, and Franklin D. Roosevelt made arrangements for post-war Europe at the Yalta Conference in February 1945. It resulted in an April meeting to form the United Nations: nation-states were created in Eastern Europe; it was agreed Poland would have free elections (in fact elections were heavily rigged by Soviets); Soviet nationals were to be repatriated, and the Soviet Union was to attack Japan within three months of Germany's surrender. The Red Army (including 78,556 soldiers of the 1st Polish Army) began its final assault on Berlin on 16 April. By now, the German Army was in full retreat and Berlin had already been battered due to preliminary air bombings. Most of the Nazi leaders had either been killed or captured. Hitler, however, was still alive, and was slowly going mad. As a final resistance effort, he called for civilians, including children, to fight the oncoming Red Army in the Volkssturm militia. When this failed, Hitler went into delusion, imagining that everyone was against him and that he still had battalions of troops to send into battle. Hitler and his staff moved into the Führerbunker, a concrete bunker beneath the Chancellery, where on 30 April 1945, he committed suicide. Admiral Karl Dönitz became leader of the German government, but the German war effort quickly disintegrated. German forces in Italy were surrendered on 2nd May1945, those in northern Germany, Denmark, and The Netherlands on the 4th May1945, and the German High Command under Generaloberst Alfred Jodl surrendered unconditionally all German forces on 7 May in Reims, France. The Western Allies celebrated "V-E Day" on 8 May and the Soviet Union "Victory Day" on 9 May.

U.S. capture of islands such as Iwo Jima and Okinawa brought the Japanese homeland within range of naval and air attack. Amongst dozens of other cities, Tokyo was firebombed, and about 90,000 people died from the initial attack. The dense living conditions around production centres and the wooden residential constructions contributed to the large loss of life. In addition, the ports and major waterways of Japan were extensively mined by air in Operation Starvation which seriously disrupted the logistics of the island nation. Later on 6 August 1945, the B-29 "Enola Gay", piloted by Colonel Paul Tibbets, dropped an atomic bomb (Little Boy) on Hiroshima, effectively destroying it. On 8 August 1945, the Soviet Union declared war on Japan, as had been agreed to at Yalta, and launched a large-scale invasion of Japanese occupied Manchuria (Operation August Storm). On 9 August, the B-29 "Bock's Car", piloted by Major Charles Sweeney, dropped an atomic bomb (Fat Man) on Nagasaki. The use of atomic weapons allowed the emperor of Japan to bypass the existing government and intervene to end the war. The new inclusion of the Soviet Union in the war may have also played a part, but in his radio address to the nation the emperor did not mention it as a major reason for the surrender of Japan. The Japanese surrendered on 15 August 1945 (V-J day), signing official surrender papers on 2 September 1945, aboard the USS Missouri in Tokyo Bay. Japan's surrender to the Allied powers did not fully end the war, however, because Japan and the Soviet Union never signed a peace agreement. In the last days of the armed conflict, the Soviet Union occupied the southern Kuril Islands, an area previously held by Japan and claimed by the Soviets. Multiple efforts to bring about a peace agreement, and officially end the war, have as of yet not succeeded.