It had been made possible by the success of Fall Gelb (Case Yellow), the invasion of the Benelux countries and northern France in the Battle of France and the encirclement of the Allied armies in the north on the Channel coast.
Hal ini telah dimungkinkan dengan keberhasilan Fall Gelb (Kasus Kuning), invasi negara Benelux dan utara Prancis dalam Pertempuran Prancis dan pengepungan tentara Sekutu di utara pantai Channel.