On September 1, 1939, Germany, led by Adolf Hitler and the Nazi Party, invaded Poland according to a secret agreement with the Soviet Union, which joined the invasion on September 17. The United Kingdom and France responded by declaring war on Germany on September 3, initiating a widespread naval war. Germany rapidly overwhelmed Poland, then Norway, the Netherlands, Belgium and France in 1940, and Yugoslavia and Greece in 1941. Italian, and later German, troops attacked British forces in North Africa. By summer 1941, Germany had conquered France and most of Western Europe, but it had failed to subdue the United Kingdom due to the success of the Royal Air Force and Royal Navy.
Germany then turned on Russia, opening a surprise attack on June 22, 1941. Despite enormous gains, the invasion became bogged down outside Moscow, in late 1941. The Russians later encircled and captured the German Sixth Army at the Battle of Stalingrad (1942-43), decisively defeated the Axis during the Battle of Kursk, and broke the Siege of Leningrad. The Red Army then pursued the retreating Wehrmacht all the way to Berlin, and won the street-by-street Battle of Berlin, as Hitler committed suicide in his underground bunker on April 30, 1945.
Meanwhile, the western Allies invaded Italy (1943) and then liberated France in 1944, following amphibious landings in the Battle of Normandy. Repulsing a German counterattack at the Battle of the Bulge in December, the Allies crossed the Rhine River and linked up with the Soviets at the Elbe River in central Germany.
During the war, six million Jews, as well as Roma and other groups, were murdered by Germany in a state-sponsored genocide known as The Holocaust.
Asia and the Pacific
Main article: Pacific War
Japan invaded China on July 7, 1937 (see Second Sino-Japanese war) with plans to expand to most of East and South-East Asia. On December 7, 1941 Japan launched surprise attacks against several countries, including the major United States Navy base at Pearl Harbor, thereby drawing the United States into the war.
After six months of sweeping successes, the Japanese were checked at the Battle of the Coral Sea and decisively defeated in the Battle of Midway, in which they lost four aircraft carriers. Japanese expansion was finally stopped and the Allies went on the offensive at the Battle of Milne Bay and the Battle of Guadalcanal, both in the Southwest Pacific. The Allies then conducted a drive across the Central Pacific, and were victorious in a series of great naval battles such as the Battle of the Philippine Sea and the Battle of Leyte Gulf in 1944, and invasions of key islands such as Iwo Jima and Okinawa in 1945. In the meantime, American submarines gradually cut off the supply of oil and other raw materials to Japan.
In the last year of the war Allied air forces conducted a strategic firebombing campaign against the Japanese homeland. On August 6, 1945, the U.S. dropped an atomic bomb on the Japanese city of Hiroshima, and on August 9 another was dropped on Nagasaki. Emperor Hirohito surrendered on August 15, 1945.
The war had many far-reaching consequences. About 62 million people, or 2.5% of the world population, died in the war, though estimates vary greatly (refer to the Casualties section). The war concluded with the surrender and occupation of Germany, Japan and Korea and recognition of the territory of Finland occupied by the Soviets. It left behind millions of displaced persons, prisoners of war, and resulted in new international boundaries. The economies of Europe, China and Japan were largely destroyed as a result of the war.
To minimize the future possibilities of the destruction and death caused by war and conflicts, the allied nations, led by the United States of America, formed the United Nations in San Francisco, California in 1945 with the hope of preventing (or at least minimizing) further conflicts.
The end of the war brought the breakup of global empires of Holland, France and Britain and the formation of new nations and alliances throughout Asia and Africa. The Philippines were granted their independence in 1946 as previously promised by the United States. Germany's and Poland's boundaries were re-drawn and Germany was split into four zones of occupation in which the three zones under the Western Allies was reconstituted as a constitutional Democracy. The empire controlled by the Soviet Union increased as they took control over most of eastern Europe as well as incorporating parts of Finland and Poland into their new boudaries. Europe was informally split into Western and Soviet spheres of influence by Soviet distrust of anything not under their control, which heightened already existing tensions between the two camps and helped form the conflict known as the Cold War.
In Asia, the Imperial Japanese Empire's government was dismantled under General Douglas McArthur and replaced by a constitutional monarchy with the emperor as a figurehead. The defeat of Japan led to the independence of Korea which was split into two parts by the Russian and American forces, marked the continuation of China's civil war and the eventual creation of the Communist People's Republic of China (PRC) on the mainland (1949) and the Nationalist Chinese (KMT) retreating to Taiwan.
World War II spawned many new technologies such as advanced aircraft, radar, jet engines, synthetic rubber and plastics, antibiotics like penicillin, helicopters, nuclear energy, rocket technology and computers. These technologies were applied to government, commercial, industrial, private and civil use.
CausesCommonly held general causes for WWII are the rise of nationalism, the rise of militarism, and the presence of unresolved territorial issues. Fascist movements emerged in Italy and Germany during the global economic instability of the 1920s, and consolidated power during the Great Depression of the 1930s. In Germany, resentment of the Treaty of Versailles — specifically article 231 (the "Guilt Clause") —, the belief in the Dolchstosslegende, and the onset of the Great Depression fueled the rise to power of the militarist National Socialist German Workers Party (the Nazi party), of which Adolf Hitler was the leader. Meanwhile, the Treaty's provisions were laxly enforced from fear of another war. Closely related was the failure of the UK and French policy of appeasement, which sought to avoid or postpone another war but actually encouraged Hitler to become bolder. The Soviet Union's signing of the Molotov-Ribbentrop Pact freed Germany of fear of reprisal from the Soviet Union when Germany invaded Poland. The League of Nations, despite its efforts to prevent the war, relied on the Great Powers to enforce its resolutions and was unable to prevent the start of the Second World War. In addition, France and Britain's prejudices when dealing with the Soviet Union before the war prevented an alliance between Western Europe and the only European power able to deter Hitler's ambitions.
Imperial Japan in the 1930s was ruled by a militarist clique of Army and Navy leaders who were devoted to Japan becoming a world colonial power (the Emperor had to personally intervene to finally terminate the war), Japan invaded Manchuria in 1931 and China in 1937 to bolster its meager stock of natural resources and extend its colonial control over a wider area. The United States and the United Kingdom reacted by making loans to China, providing covert military assistance, pilots and fighter aircraft to Kuomintang China and instituting increasingly broad embargoes of raw materials and oil against Japan. These embargoes would potentially have eventually forced Japan to give up its newly conquered possessions in China or find new sources of oil and other materials to run their economy. Japan was faced with the choice of withdrawing from China, negotiating some compromise, developing new sources of supply, buying what they needed some where else, or going to war to conquer the territories that contained oil, bauxite and other resources in the Dutch East Indies, Malay and the Philippines. Believing the French, Dutch and British governments were more than occupied with the war in Europe, the Soviets were reeling from German attacks and The United States could not be organized for war for years and would seek a compromise before waging full scale war they chose the latter, and went ahead with plans for the Greater East Asia War in the Pacific. They gambled they could pick up a new expanded empire for Japan.  The direct cause of the war with Japan was the sneak attack on Pearl Harbor, Singapore and the Philippines December 7, 8 1941. Germany, thinking the United States would be more than occupied with fighting the Japanese, declared war on the United States December 12 1941.
Main article: Timeline of World War II
Main articles: The Holocaust, End of World War II in Europe, and Strategic bombing during World War II
War breaks out: 1939
Main articles: Appeasement, Franco-Polish Military Alliance, Polish-British Common Defence Pact, Munich Agreement, and Molotov-Ribbentrop Pact
German policy aims and ideologies
The chief stated aim of the German policy at the time was the reacquisition of German territories taken by the Treaty of Versailles, and the addition of ethnic German regions of former Austria-Hungary to form a Greater Germany.
Hitler's real agenda was clearly the takeover of neighboring countries. In fact, when he annexed Czechoslovakia in the previous year, without any conflict due to England's intervention, he complained that he had been deprived of the triumphal war which he sought. The invasion of Poland was one step in an overall campaign of re-militarization, and preparation of the German people for renewed warfare. 
However, German foreign policy professed concern for the rights of ethnic Germans living in portions of Poland and Czechoslovakia which had been taken from Germany and Austria respectively. During his negotiations with Chamberlain, Hitler mentioned their plight as one of his key reasons for asserting claims to portions of these countries.
During one session with UK Prime Minister Neville Chamberlain, Hitler's aides brought him multiple reports alleging atrocities against ethnic Germans in nearby countries, which Hitler invoked in support of Germany's claims to its former territory.
When Hitler annexed parts of Czechoslovakia and Poland, he was welcomed enthusiastically by these ethnic Germans. When the war ended, many of these communities were forcibly compelled to return to Germany proper.
Another of the main reasons that German society moved towards war was due to the perceived inequities of the Versailles Treaty. More than anything else, this enabled the Nazis to make the case that only they could free Germany from international subjugation. Hitler remilitarized the Rhineland and the Ruhr, and overturned several territorial dispositions which were enacted by the treaty. In fact, the Versailles Treay did arguably constitute a uniquely excessive burden on Germany, in that the treaty did deprive Weimar Germany of many of the tools and conditions which would have enabled it to function as a viable state.
In the hands of the Nazis, this issue was used to rationalize brutal persecution of entire ethnic minorities and political groups. This effort against previous international settlements enabled a convergence of their political programs, war aims, and racist ideologies.
Molotov signs the Molotov-Ribbentrop Pact in Moscow. Behind him are Shaposhnikov, Ribbentrop, and Stalin.Appeasement and Pre-war alliances
The British and French governments followed a policy of appeasement in order to avoid a new European war. This was partially due to doubts about the willingness of their populations to fight another war so soon after the huge death tolls of the first World War. This policy culminated in the Munich Agreement in 1938, in which the seemingly inevitable outbreak of the war was averted when the United Kingdom and France agreed to Germany's annexation and immediate occupation of the German-speaking regions of Czechoslovakia. Chamberlain declared that the agreement represented "peace in our time". In March 1939, Germany invaded the rest of Czechoslovakia, effectively killing appeasement. Less than a year after the Munich agreement, the United Kingdom and France declared war on Germany.
The failure of the Munich Agreement showed that deals made with Hitler at the negotiating table could not be trusted and that his aspirations for power and dominance in Europe went beyond anything that England and France would tolerate. Poland and France pledged on May 19, 1939, to provide each other with military assistance in the event either was attacked. The British had already offered support to Poland in March. On August 23, 1939, Germany and the Soviet Union signed the Molotov-Ribbentrop Pact. The Pact included a secret protocol that would divide Central Europe into German and Soviet areas of interest, including a provision to partition Poland. Each country agreed to allow the other a free hand in its area of influence, including military occupation. The deal provided for sales of oil and food from the Soviets to Germany, thus reducing the danger of a UK blockade such as the one that had nearly starved Germany in World War I. Hitler was then ready to go to war with Poland and, if necessary, with the United Kingdom and France. He claimed there were German grievances relating to the issues of the Free City of Danzig and the Polish Corridor, but he planned to conquer all Polish territory and incorporate it into the German Reich. The signing of a new alliance between the United Kingdom and Poland on August 25 did not significantly alter his plans.
On September 1, 1939, Germany invaded Poland, using the false pretext of a faked "Polish attack" on a German border post.
On September 3, the United Kingdom and France declared war on Germany, followed quickly by Canada, Australia, and New Zealand.
The French mobilized slowly and then mounted only a token offensive in the Saar, which they soon abandoned, while the British could not take any direct action in support of the Poles in the time available (see Western betrayal). Meanwhile, on September 8, the Germans reached Warsaw, having slashed through the Polish defenses.
On September 17, the Soviet Union, pursuant to its secret agreement with Germany, invaded Poland from the east, throwing Polish defences into chaos by opening the second front. A day later, both the Polish president and commander-in-chief fled to Romania. On October 1, hostile forces, after a one-month siege of Warsaw, entered the city. The last Polish units surrendered on October 6. Poland, however, never officially surrendered to the Germans. Some Polish troops evacuated to neighboring countries. In the aftermath of the September Campaign, occupied Poland managed to create a powerful resistance movement and contributed significant military forces to the Allies for the duration of World War II
Main article: Phony War
After Poland fell, Germany paused to regroup during the winter of 1939-1940 until April 1940, while the British and French stayed on the defensive. The period was referred to by journalists as “the Phony War” or the “Sitzkrieg” because so little ground combat took place.
Battle of the Atlantic
Meanwhile in the North Atlantic, German U-boats operated against Allied shipping. The submarines made up in skill, luck, and courage what they lacked in numbers. One U-boat sank the British carrier HMS Courageous, while another U-boat managed to sink the battleship HMS Royal Oak in its home anchorage of Scapa Flow. Altogether, the U-boats sank more than 110 vessels in the first four months of the war. The most damaging effect of the U-boats was in sinking transatlantic merchant shipping.
After 1943, Germany had no serious chance of victory at sea. The Allies produced ships faster than they were sunk, and lost fewer ships by adopting the convoy system. Improved anti-submarine warfare meant that the life expectancy of a typical U-boat crew would be measured in months. The vastly improved Type 21 U-boat appeared as the war was ending, but too late.
In the South Atlantic, the Admiral Graf Spee sank nine UK Merchant Navy vessels. She was then engaged by British cruisers HMS Ajax, HMS Exeter, and HMNZS Achilles in the Battle of the River Plate, and forced into Montevideo Harbor. Rather than face battle again, Captain Langsdorff made for sea and scuttled his battleship just outside the harbor.
Main article: Second Sino-Japanese War
The Second Sino-Japanese War began in 1937, when Japan attacked deep into China from its foothold in Manchuria. On July 7, 1937, Japan, after occupying Manchuria since 1931, launched another attack against China near Beiping (now Beijing). The Japanese made initial advances but were stalled in the Battle of Shanghai. The city eventually fell to the Japanese in December 1937, and the capital city Nanjing (Nanking) also fell. As a result, the Chinese government moved its seat to Chongqing for the remainder of the war. The Japanese forces committed brutal atrocities against civilians and prisoners of war in the Rape of Nanking, slaughtering as many as 300,000 civilians within a month.
Second Russo-Japanese War
Main article: Battle of Khalkhin Gol
On May 8, 1939, 700 Mongol horsemen crossed the Khalka river, which the Japanese considered to be the Manchurian border. The Soviet and Mongolian governments believed the border was twenty miles to the east. Mongol and Manchu forces began to shoot at each other, and within days their Soviet and Japanese patrons had sent large military contingents, which almost immediately joined in the clash, which led to a full-scale war which lasted well into September, and Soviet fear of having to fight a two front war was a primary reason for the Molotov-Ribbentrop Pact with the Nazis. The Japanese would suffer approximately 18,000 casualties, the Soviet-Mongolian forces 9,000.
War spreads: 1940
Soviet-Finnish War and occupation of Baltic Republics
Main articles: Winter War and Occupation of Baltic Republics
In a secret Soviet-German agreement, Finland was designated a Soviet buffer zone, and the Soviets attacked on November 30, 1939, which started the Winter War. Despite outnumbering Finnish troops by 4 to 1, the Red Army found the attack embarrassingly difficult, and the Finnish defence prevented an all-out invasion. Finally, however, the Soviets prevailed and the peace treaty saw Finland cede strategically important border areas near Leningrad. The war triggered an international outcry, and, on December 14, the Soviet Union was expelled from the League of Nations. In June 1940, the Soviet Union occupied Latvia, Lithuania, and Estonia, sending the local leadership to the Gulag; in addition, it annexed Bessarabia and Northern Bukovina from Romania.
German invasion of Denmark and Norway
Main article: Norwegian Campaign
Germany invaded Denmark and Norway on April 9, 1940, in Operation Weserübung, in part to counter the threat of an impending Allied invasion of Norway. Denmark did not resist, but Norway fought back. The United Kingdom, whose own invasion was ready to launch, landed in the north. By late June, the Allies were defeated and withdrew, Germany controlled most of Norway, and the Norwegian Army had surrendered, while the royal family escaped to London. Germany used Norway as a base for air and naval attacks on Arctic convoys headed to the Soviet Union.
German invasion of France and the Low Countries
Main articles: Battle of France and Battle of the Netherlands
On May 10, 1940, the Germans invaded Luxembourg, Belgium, the Netherlands, and France, ending the Phony War. The British Expeditionary Force (BEF) and the French Army advanced into northern Belgium and planned to fight a mobile war in the north, while maintaining a static continuous front along the Maginot Line further south. The Allied plans were immediately smashed by the most classic example in history of Blitzkrieg. The Dutch city of Rotterdam was destroyed in a bombing raid.
In the first phase of the invasion, Fall Gelb (CACA), the Wehrmacht's Panzergruppe von Kleist, raced through the Ardennes, a heavily forested region which the Allies had thought impenetrable for a modern, mechanized army. The Germans broke the French line at Sedan, held by reservists rather than first-line troops, then drove west across northern France to the English Channel, splitting the Allies in two. Meanwhile, Belgium, Luxembourg, and the Netherlands fell quickly following the attack of German Army Group B.
The BEF and French forces, encircled in the north, were evacuated from Dunkirk in Operation Dynamo. The operation was one of the biggest military evacuations in history, as 338,000 British and French troops were transported across the English Channel on warships and civilian boats.
On June 10, Italy joined the war, attacking France in the south. German forces then continued the conquest of France with Fall Rot (Case Red). France signed an armistice with Germany on June 22, 1940, leading to the direct German occupation of Paris and two-thirds of France, and the establishment of a neutral (but pro-German) state headquartered in southeastern France known as Vichy France.
Battle of Britain
Main article: Battle of Britain
Germany had begun preparations in summer of 1940 to invade the United Kingdom in Operation Sea Lion. Most of the UK Army's heavy weapons and supplies had been lost at Dunkirk. The Germans had no hope of overpowering the Royal Navy, but they did think they had a chance of success, if they could gain air superiority. To do that, they first had to deal with the Royal Air Force. The ensuing contest in the late Summer of 1940 between the two air forces became known as the Battle of Britain. The Luftwaffe initially targeted RAF Fighter Command aerodromes and radar stations. Hitler, angered by retaliatory UK bombing raids on Berlin, switched his attentions towards the bombing of London, in an operation known as The Blitz. The Luftwaffe was eventually beaten back by Hurricanes and Spitfires, while the Royal Navy remained in control of the English Channel. Thus, the invasion plans were cancelled indefinitely, as Hitler turned to the East.
Italian invasion of Greece
Main articles: Greco-Italian War, Battle of Greece, and Battle of Taranto
Italy invaded Greece on October 28, 1940, from Italian occupied Albania. The Greek army forced the Italians to retreat back to Albania. By mid-December, the Greeks occupied one-quarter of Albania, tying down 530,000 Italians. Meanwhile, in fulfillment of Britain's guarantee to Greece the Royal Navy struck at the Italian fleet. Torpedo bombers from British Aircraft Carriers attacked the Italian fleet in the southern port of Taranto. One battleship was sunk and several other ships were put temporarily out of action. The success of aerial torpedoes at Taranto was noted with interest by Japan's naval chief, Yamoto, who was considering ways of "taking out" the U.S. Pacific fleet.
Main articles: North African Campaign and East African Campaign (World War II)
With the French fleet neutralized, the UK Royal Navy battled the Italian fleet for supremacy in the Mediterranean. The British had strong bases at Gibraltar, Malta, and Alexandria, Egypt. In Africa, Italian troops invaded and captured British Somaliland in August. In September, the North African Campaign began when Italian forces in Libya attacked British forces in Egypt. The aim was to capture the Suez Canal, a vital link between the United Kingdom and India. UK, Indian, and Australian forces counter-attacked in Operation Compass, but this offensive stopped in 1941 when much of the Australian and New Zealand forces were transferred to Greece to defend it from German attack. German forces (known later as the Afrika Korps) under General Erwin Rommel, however, landed in Libya and renewed the assault on Egypt.
By 1940, the war had reached a stalemate with both sides making minimal gains. The United States provided heavy financial support for China and set up the Flying Tigers air unit to bolster Chinese air forces.
Japanese forces invaded northern parts of French Indo-China on September 22. The move was not unexpected, and followed a demand for bases in the region made two months earlier. Japanese relations with the west had deteriorated steadily in recent years and United States, having renounced the U.S.-Japanese trade treaty of 1911, placed embargoes on exports to Japan of war and other materials.
War becomes global: 1941
Main article: Lend-Lease
After France had fallen in 1940, the United Kingdom was out of money. Franklin Roosevelt persuaded the U.S. Congress to pass the Lend-Lease act on March 11, 1941, which provided the United Kingdom and 37 other countries with US$50 billion dollars in military equipment and other supplies, US$31.4 billion of it going to the United Kingdom and the Commonwealth.
Canada operated a similar program that sent $4.7 billion in supplies to the United Kingdom and the Soviet Union.
German invasion of Yugoslavia and Greece
Main articles: Invasion of Yugoslavia and Battle of Greece
On April 6, 1941, German, Italian, Hungarian, and Bulgarian forces invaded Yugoslavia, ending with the surrender of the Yugoslavian army on April 17, and the creation of a puppet state in Croatia. Two rival resistance movements endured in Yugoslavia for the remainder of the war. The Communist group, AVNOJ, led by Tito finally prevailed over the Chetniks led by Draža Mihailović. Also on April 6, Germany invaded Greece from Bulgaria. Greek troops put up a brave fight, but the army was outnumbered and collapsed. Athens fell on April 27, yet the United Kingdom managed to evacuate over 50,000 troops. The stubborn Greek resistance and the attack on Yugoslavia, however, delayed the German invasion of the Soviet Union by a critical six weeks.
German airborne invasion of Crete
Main article: Battle of Crete
Nazi Germany invaded the island with soldiers from the elite divisions of the 7th Flieger Division and 5 Mountain Division. Crete was defended by about 11,000 Greek and 28,000 ANZAC troops (see Creforce), who had just escaped Greece without their artillery or vehicles. The Germans attacked the three main airfields of the island of Maleme, Rethimnon, and Heraklion. After one day of fighting, none of the objectives were reached and the Germans had suffered appalling casualties. German plans were in disarray and Commanding General Kurt Student was contemplating suicide. During the next day, through miscommunication and failure of Allied commanders to grasp the situation, Maleme airfield in western Crete fell to the Germans. The loss of Maleme enabled the Germans to fly in heavy reinforcements and overwhelm the Allied forces on the island. In light of the heavy casualties suffered by the parachutists, however, Adolf Hitler forbade further airborne operations.
German invasion of the Soviet Union
Main articles: Operation Barbarossa, Eastern Front (World War II), and Continuation War
From the signing of the Molotov-Ribbentrop Pact in August, 1939, through half of 1941, Stalin and the Soviet Union fed and equipped Hitler and Germany as Germany invaded Western Europe and attacked the United Kingdom by air. Germany then betrayed its Soviet partner.
On June 22, 1941, Operation Barbarossa began, the largest military invasion in history. Three German Army Groups, an Axis force of over four million men, advanced rapidly deep into the Soviet Union, destroying almost the entire western Red Army in huge battles of encirclement. Nevertheless, the Soviets dismantled as much industry as possible ahead of the advancing Axis forces, moving it to areas east of the Ural Mountains for reassembly, and ultimately resupplying the Soviet armies and contributing mightily to the destruction of Germany. By late November, the Axis had reached a line at the gates of Leningrad, Moscow, and Rostov, at the cost of about 23 percent casualties. Their advance then ground to a halt as the harsh Russian winter set in. The German General Staff had underestimated the size of the Soviet army and its ability to draft new troops. German soldiers were ill-equipped for harsh weather, and logistics were poor because of the distances, the rudimentary rail and road system, and the breakdown of men, animals and machinery in extreme cold.
and theres alot more but i'm to tired to write more lol.........