The Second World War, often abbreviated as WWII or WW2, was a global military conflict that took place from 1939 to 1945. It was the most extensive and devastating war in human history, involving most of the world's nations and divided into two major military alliances: the Allies and the Axis powers. The conflict began on September 1, 1939, when Nazi Germany, led by Adolf Hitler, invaded Poland. In response to Germany's aggression, Britain and France declared war on Germany two days later, marking the official start of the war. The Axis powers, which included Germany, Italy, and Japan, aimed to establish authoritarian regimes and expand their territories through military conquest. The Allies, on the other hand, sought to defend democracy and curb the aggressive expansion of the Axis powers.The war came to an end on September 2, 1945, when Japan formally surrendered aboard the USS Missouri, marking Victory over Japan Day (V-J Day). The Second World War resulted in over 70 million casualties, including military personnel and civilians, and had a profound impact on global politics, economics, and society. It prompted the formation of international organizations like the United Nations to prevent future conflicts and promote peace and cooperation among nations.