World War II began on this date when Nazi Germany, under Adolf Hitler, invaded Poland. This act of aggression prompted the United Kingdom and France to declare war on Germany on September 3, 1939, marking the official start of the war in Europe. The invasion was a direct result of the Molotov-Ribbentrop Pact between Germany and the Soviet Union, which divided Poland between the two powers.

Following a series of military victories, Germany invaded and conquered France in June 1940. This led to the establishment of the Vichy French government and marked a significant expansion of German control over continental Europe. The fall of France shifted the focus of the war, with the British Empire continuing to resist German forces, particularly in the aerial Battle of Britain and the naval Battle of the Atlantic.

Germany launched a massive invasion of the Soviet Union, known as Operation Barbarossa, which opened the Eastern Front. This campaign initially resulted in large territorial gains for Germany but ultimately proved to be a costly and decisive mistake, as the Soviet Union managed to resist and eventually push the German forces back.

The Japanese launched a surprise attack on the United States naval base at Pearl Harbor, Hawaii, drawing the United States into the war. This attack led to the United States declaring war on Japan, and subsequently, Germany and Italy declaring war on the United States, expanding the global scope of the conflict.

The Allies launched a massive invasion of Nazi-occupied France, known as D-Day, which marked a crucial turning point in the war. The successful landing and establishment of a foothold in Normandy paved the way for the liberation of Western Europe from German control.

As Allied forces closed in on Berlin, Adolf Hitler committed suicide. Shortly after, on May 7, 1945, Germany unconditionally surrendered, marking the end of the war in Europe. This event, known as V-E Day (Victory in Europe Day), was celebrated on May 8, 1945.

The United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki, leading to unprecedented destruction and loss of life. These bombings played a significant role in Japan's decision to surrender, bringing an end to the war in the Pacific.

Japan formally surrendered to the Allied Powers on board the USS Missouri in Tokyo Bay, marking the official end of World War II. This ceremony was led by General Douglas MacArthur, who would later oversee the occupation and reconstruction of Japan.