World War II, also referred to as WWII, World War 2, or the Second World War, started on September 1, 1939. World War II altered the political alignment and social structure of the world. It involved 7 countries.

Germany invaded Poland on September 1, 1939. The Nazi leader of the Germans claimed the massive invasion was a defensive action, but Britain and France were not convinced. Britain and France declared war on Germany two days later, in retaliation.

Adolf Hitler was born on April 20, 1889, in what was then known as Austria-Hungary. Hitler claimed the massive invasion was a defensive action and that Germany invaded western Poland under the pretext of having been denied claims to the Free City of Danzig and the right to extraterritorial roads across the Polish Corridor, which Germany had ceded under the Versailles Treaty. To Hitler, the conquest of Poland would bring Lebensraum, or “living space,” for the German people.

Hitler ruled Germany from 1933-1945. Hitler governed by a dictatorship under the control of the Nazi Party (NSDAP). Under Hitler's rule, Germany was transformed into a fascist state in which the Nazi Party took totalitarian control over nearly all aspects of life.

Hitler looked to expand the Greater Germanic Reich by invading Poland. Hitler proclaimed his vision of a united empire of Germanic nations of Europe in which the Dutch, Flemish, and Scandinavians were joined into a "racially pure" polity under German leadership.

China and Japan were already at war when WWII began. The Second Sino-Japanese War was a military conflict, fought primarily between the Republic of China and the Empire of Japan, from 1937 to 1945. China fought Japan with some economic help from Germany, the Soviet Union, and the United States.

There were over 100 million people from over 30 countries involved in WWII. The two main alliances were divided between the Allies and the Axis powers. The major participants threw their entire economic, industrial, and scientific capabilities behind the war effort, erasing the distinction between civilian and military resources.

The Battle of the Atlantic was the longest battle in WWII. It lasted from 1939 to1945. It pitted U-boats and other warships of the Kriegsmarine (German Navy) and aircraft of the Luftwaffe (German Air Force) against the Royal Canadian Navy, Royal Navy, the United States Navy, and Allied merchant shipping.

The Battle of the Bulge was the deadliest battle for American Troops in WWII. There were more than 80,000 American casualties. It was the last major German offensive campaign of World War II.

General Patton's command included the 761st Black Panthers, the first black tank unit to join the combat. The Battle of the Bulge was launched through the densely forested Ardennes region of Wallonia in Belgium, France, and Luxembourg, on the Western Front, towards the end of World War II, in the European theatre. It was the deadliest US battle in WWII.

The Nazis murdered approximately 12 million people. Racism, especially antisemitism, was a central feature of the Nazi regime. Nearly half of those killed were Jews, in the Holocaust.

The offensives in Poland and France taught the English-speaking world a new word - Blitzkrieg - which means lighting war. It was a military tactic designed to create disorganization among enemy forces through the use of mobile forces and locally concentrated firepower. Its successful execution results in short military campaigns.

The swastika was originally an ancient religious symbol. It derives from the Sanskrit name for a hooked cross, which was used by ancient civilizations as a symbol of fertility and good fortune. It has been found in the ruins of Greece, Egypt, China, India, and Hindu temples.

Between 1939 and 1945, the Allies dropped 3.4 million tons of bombs. This averaged to 27,700 tons per month. They led a strong offence.

The Soviet Union was the country with the largest number of WWII casualties. The country lost over 21 million people - over 15% of its population. The Soviet Union was in existence from 1922 until 1991.

The Soviet Union sought to claim parts of Finnish territory, demanding that Finland cede substantial border territories in exchange for land elsewhere. The result was a Soviet invasion of Finland on November 30, 1939, three months after the outbreak of World War II. It finally ended with the Moscow Peace Treaty on March 13, 1940.

The Battle of Britain was a battle to defend the United Kingdom (UK) against the German Air Force (Luftwaffe) attacks from the end of June 1940. It was a decisive battle after France had fallen to Germany. This was a significant turning point of World War II, as Germany’s Luftwaffe failed to gain air superiority over the Royal Air Force despite months of targeting Britain’s air bases.

From 1940-1945, the U.S. defense budget increased from $1.9 billion to $59.8 billion. In modern-day figures, for 2017, the total US government spending for defense (including military defense, veterans affairs, and foreign policy) is budgeted to be $853.6 billion.

Pearl Harbor was attacked by the Japanese on December 7, 1941. At the time of the Pearl Harbor attack, there were 96 ships anchored. Eighteen ships were sunk or seriously damaged, including eight battleships. There were 2,402 American men killed and 1,280 injured.

The U.S.S Arizona still lies at the bottom of Pearl Harbour today. After a bomb detonated in a powder magazine, the battleship exploded violently and sank, with the loss of 1,177 officers and crewmen. Unlike many of the other ships sunk or damaged that day, Arizona was irreparably damaged by the force of the magazine explosion, though the Navy removed parts of the ship for reuse.

The Battle of the Coral Sea was a major battle between Japan and the United States. The battle occurred from May 4-8, 1942. It was the first action in which aircraft carriers engaged each other, as well as the first in which neither side's ships sighted or fired directly upon the other.

The Luftwaffe was the aerial warfare branch of the German Wehrmacht. Led by Hermann Goering, it became the largest and most powerful in Europe by the start of World War II. In modern times, it is the fourth largest air force within the European Union, after the air forces of the United Kingdom, France and Italy.

During WWII, hamburgers in the U.S. were dubbed Liberty Steaks, to avoid the German-sounding name. Anti-German sentiment was no less present in America during World War I than it was during World War II, and many people wanted their language to be less German and more American.

The Manhattan Project was a secret military program, created in 1942, to produce the first US nuclear weapon. Fears that Nazi Germany would build and use a nuclear weapon during World War II triggered the start of the Manhattan Project, which was originally based in Manhattan, New York.

On August 6, 1945, an American B-29 bomber dropped the world’s first deployed atomic bomb over the Japanese city of Hiroshima. The explosion wiped out 90 percent of the city and immediately killed 80,000 people; tens of thousands more would later die of radiation exposure. Three days later, a second B-29 dropped another A-bomb on Nagasaki, killing an estimated 40,000 people.

The now iconic We Can Do It poster was initially not intended for public display. Only a small number of people saw it when it was first published in 1942. It only gained popularity in the 1980s, when the feminist movement appropriated the image.

On December 8, 1941, Britain and the U.S. declared war on Japan. On December 11, Germany declared war on the U.S. The U.S. is the only nation Germany formally declared war on.

The Soviets introduced a new weapon, the Katyusha, which could fire 320 rockets in 25 seconds. More than 50 years later, the Katyusha remains an effective weapon.

WWII was the most destructive conflict in history. It cost more money, damaged more property, killed more people, and caused more far-reaching changes than any other war in history.

Prisoners of war in Russian camps experienced an 85% mortality rate. The quantity, to say nothing of the quality, of the food received by the Soviet POWs was set far below the minimum required for human survival.

After World War II, Nazi Germany west of the Oder-Neisse line was divided into four occupation zones. They were occupied four ways by the Allied powers -- the Soviet Union, the United Kingdom, and the United States -- and by France. This was done for administrative purposes from 1945 to 1949.

Italy was the first Axis partner to give up in WWII. It surrendered to the Allies on September 8, 1943. This was six weeks after leaders of the Italian Fascist Party deposed Fascist leader and Italian dictator Benito Mussolini.

The goal of the Yalta Conference was to shape a post-war peace that represented not just a collective security order, but also a plan to give self-determination to the liberated peoples of post-Nazi Europe. Among the issues discussed at the Yalta Conference were German war reparations, the division of Germany into zones of occupation, and the repatriation of all Soviet soldiers who had joined American and British troops, whether they were willing to return or not. It is believed that many of these soldiers were put to death upon their return to Soviet control.

WWII casualties totaled between 50-70 million. More than 80% of this total came from four countries: Russia, China, Germany, and Poland. More than half of these casualties were civilians, most of whom were women and children.

Victory in Europe Day, generally known as V-E Day, VE Day, or simply V-Day, was the public holiday celebrated on May 8, 1945, to mark the formal acceptance by the Allies of World War II of Nazi Germany's unconditional surrender of its armed forces. The Japanese representatives aboard the USS Missouri surrendered on September 2, 1945. Victory over Japan Day, also known as Victory in the Pacific Day, V-J Day, or V-P Day, is the day on which Japan surrendered, in effect ending WWII once and for all.