World War II was the biggest and deadliest war in history. From 1939 to 1945, more than 50 nations fought across the globe as some nations invaded others to expand their own borders. World War II explores the causes, leaders, and major battles of this conflict, while also exploring its outcomes and legacy today. Aligned to Common Core Standards and correlated to state standards. Core Library is an imprint of Abdo Publishing, a division of ABDO.