In three sentences:
World War 2 began in 1939 when Germany invaded Poland, leading Britain and France to declare war on Germany. Key events in the following years included Germany conquering France in 1940, the US entering the war in 1941 after Pearl Harbor, and the Allied invasion of German-occupied France on June 6, 1944 known as D-Day, which involved over 160,000 troops crossing the English Channel to storm Normandy's beaches and fight German forces. D-Day marked a major turning point in the war, as it launched the Allied forces' successful campaign to liberate Western Europe from Nazi control.