The Eastern provinces were relatively easy overrun because they had deliberately left lightly defended in order to create the necessary strategic depth. Adolf Hitler, who had expected the occupation to be completed in two hours (sic!) and maximally two days (the invasion of Denmark in April 1940 had taken only one day), ordered Rotterdam to be annihilated to force a breakthrough as the attack was clearly failing on all fronts, leading to the Rotterdam Blitz on 14 May that destroyed much of the city centre and killed about 800 people; it also left some 85,000 homeless. Furthermore, the Germans threatened to destroy every other major historical city until the Dutch Forces accepted capitulation.