The Second World War, also known as World War II, was a global conflict that occurred from 1939 to 1945. It involved many countries and had a profound impact on the world. It was fought between two major alliances: the Allies, including the United States, United Kingdom, and Soviet Union, and the Axis powers, including Germany, Italy, and Japan. The war was characterized by significant military advancements, devastating battles, and the Holocaust. It ultimately led to the defeat of the Axis powers and the reshaping of the post-war world. It's a complex and important part of history to study and understand.