On 10 May, Germany invaded France, Belgium, Holland, and Luxembourg and quickly defeated them by using blitzkrieg tactics. The British were forced to leave mainland Europe at Dunkirk. On June 10, Italy invaded France, declaring war on France and the United Kingdom. Soon after that, France was divided into occupation zones. One was directly controlled by Germany and Italy, and the other was unoccupied Vichy France.
By June 1940, the Soviet Union moved its soldiers into the Baltic states and took them, followed by Bessarabia in Romania. Although there had been some collaboration between the Soviet Union and Germany earlier, this event made it serious. Later, when the two could not agree to work more closely together, relationships between them became worse to the point of war.
Then Germany began an air battle over Britain to prepare for a landing on the island, but the plan was finally canceled in September. The German Navy destroyed many British ships transporting goods in the Atlantic. Italy, by this time, had begun its operation in the Mediterranean. The United States remained neutral but started to help the Allies. By helping to protect British ships in the Atlantic, the United States found itself fighting German ships by October 1941 but this was not officially war.
In September 1940, Italy began to invade British-held Egypt. In October, Italy invaded Greece, but it only resulted in an Italian retreat to Albania. Again, in early 1941, an Italian army was pushed from Egypt to Libya in Africa. Germany soon helped Italy. Under Rommel's command, by the end of April 1941, the Commonwealth army was pushed back to Egypt again. Other than North Africa, Germany also successfully invaded Greece, Yugoslavia and Crete by May. Despite these victories, Hitler decided to cancel the bombing of Britain after 11 May.
At the same time, Japan's progress in China was still not much, although the nationalist and communist Chinese began fighting each other again. Japan was planning to take over European colonies in Asia while they were weak, and the Soviet Union could feel a danger from Germany, so a non-aggression pact (which was an agreement that both countries would not attack each other) between the two was signed in April 1941. However, Germany kept preparing an attack on the Soviet Union, moving its soldiers close to the Soviet border.
On June 22, 1941, the European Axis countries attacked the Soviet Union. During the summer, the Axis quickly captured Ukraine and the Baltic regions, which caused huge damage to the Soviets. Britain and the Soviet Union formed a military alliance between them in July. Although there was great progress in the last two months when winter arrived, the tired German army was forced to delay its attack just outside Moscow. It showed that the Axis had failed its main targets, while the Soviet army was still not weakened. This marked the end of the blitzkrieg stage of the war.
By December, the Red Army facing the Axis army had received more soldiers from the east. It began a counter-attack that pushed the German army to the west. The Axis lost a lot of soldiers but it still saved most of the land it received before.
By November 1941, the Commonwealth counter-attacked the Axis in North Africa and got all the land it lost before. However, the Axis pushed the Allies back again until stopped at El Alamein.
In Asia, German successes encouraged Japan to call for oil supplies from the Dutch East Indies. Many Western countries reacted to the occupation of French Indochina by banning oil trading with Japan. Japan planned to take over European colonies in Asia to create a great defensive area in the Pacific so that it could get more resources. But before any future invasion, it first had to destroy the American Pacific Fleet in the Pacific Ocean. On December 7, 1941, it attacked Pearl Harbor as well as many harbors in several South East Asian countries. This event led the United States, United Kingdom, Australia, Western Allies and China to declare war on Japan, while the Soviet Union remained neutral. Most of the Axis nations reacted by declaring war on the United States.
By April 1942, many southeast Asian countries: Burma, Malaya, the Dutch East Indies, and Singapore, had almost fallen to the Japanese. In May 1942, the Philippines fell. The Japanese navy had many quick victories. But in June 1942, Japan was defeated at Midway. Japan could not take more land after this because a large part of its navy was destroyed during the battle.
Japan then began its plan to take over Papua New Guinea again, while the United States planned to attack the Solomon Islands. The fight on Guadalcanal began in September 1942 and involved a lot of troops and ships from both sides. It ended with the Japanese defeat in early 1943.
On the Eastern Front, the Axis defeated Soviet attacks during summer and began its own main offensive to southern Russia along Don and Volga Rivers in June 1942, trying to take over oil fields in Caucasus, critical to the Axis for fueling their war effort, and a great steppe. Stalingrad was in the path of the Axis army, and the Soviets decided to defend the city. By November the Germans had nearly taken Stalingrad, however, the Soviets were able to surround the Germans during winter After heavy losses, the German army was forced to surrender the city in February 1943. Even though the front was pushed back further than it was before the summer attacks, the German army still had become dangerous to an area around Kursk. Hitler devoted almost two-thirds of his armies to The Battle of Stalingrad. The Battle of Stalingrad was the largest and deadliest battle in this world's time.
In August 1942, because of the Allied defense at El Alamein, the Axis army failed to take the town. A new Allied offensive, drove the Axis west across Libya a few months later, just after the Anglo-American invasion of French North Africa forced it to join the Allies. This led to Axis defeat in the North African Campaign May 1943.
In the Soviet Union, on July 4, 1943, Germany started an attack around Kursk. Many German soldiers were lost because of the Soviets' well-created defenses. Hitler canceled the attack before any clear outcome. The Soviets then started their own counter-attack, which was one of the turning points of the war. After this, the Soviets became the attacking force on the Eastern Front, instead of the Germans.
On July 9, 1943, affected by the earlier Soviet victories, the Western Allies landed on Sicily. This resulted in the arrest of Mussolini in the same month. In September 1943, the Allies invaded mainland Italy, following the Italian armistice with the Allies. Germany then took control of Italy and disarmed its army, and built up many defensive lines to slow the Allied invasion down. German special forces then rescued Mussolini, who then soon created the German-occupied client state, Italian Social Republic.
Late in 1943 Japan conquered some islands in India and began an invasion of the Indian mainland. The Army of India and other forces expelled them in early 1944.
In early 1944, the Soviet army drove off the German army from Leningrad, ending the longest and deadliest siege in history. After that, the Soviets began a big counter-attack. By May, the Soviets had retaken Crimea. With the attacks in Italy from September 1943, the Allies succeeded in capturing Rome on June 4, 1944, and made the German forces fall back.