World War II was a global conflict whose effects reached far beyond the battlefield. It transformed political borders, accelerated technological change, displaced millions, and helped create a new international order.
Studying the war responsibly means holding several scales together: decisions by governments, the experience of civilians, the violence of occupation, resistance, genocide, and the difficult political settlements that followed. The past remains relevant because its institutions and wounds continue to shape the present.
Further reading: Encyclopaedia Britannica