On 1 September 1939, Germany invaded Poland. It was the start of a conflict that would erupt over every continent, see the deaths of tens of millions of people, much of central Europe destroyed, the development of jets, ballistic missiles and computers as well as the atomic bomb. 1940 saw the conquest by Nazi Germany of Denmark, Norway, Belgium, the Netherlands, Luxembourg and France, all involving heavy use of airpower, either transporting troops or closely supporting the armoured forces on the ground. Later that summer, RAF Fighter Command would defend Britain against the Luftwaffes drive for air superiority over the English Channel, and in the autumn the Blitz against London and other British cities would begin. After a period of Phoney War, 1940 saw the war in the air begin in earnest.