The "X documents" and how to interpret them played a key role in the debate in the late 1980s between Overy and the Marxist Timothy Mason about whether the German attack on Poland was a "flight into war" forced on Hitler by an economic crisis. Other historians have contended that Goerdeler's information about German economic problems was correct and have pointed to the fact that only massive Soviet economic support, combined with plundering occupied lands, saved the German economy from collapse during the winter of 1939–40. Even with Soviet economic support (especially oil) and the exploitation of Poland and the "Reich" Protectorate of Bohemia-Moravia, the impact of the British blockade caused a 75% decline in value and tonnage of German imports during the Phoney War.