closed 160 km (100 mi) east, near Brst. On that day, too, the Soviet Red Army lunged across the border. By September 20, practically the whole country was in German or Soviet hands, and only isolated pockets continued to resist. The last to surrender was the fortress at Kock, on October The Blitzkrieg in Poland
             Polish strategic doctrine called for a rigid defense of the whole frontier and anticipated several weeks of preliminary skirmishing. It was wrong on both counts. On the morning of September 1, waves of German bombers hit the railroads and hopelessly snarled the Polish mobilization. In four more days, two army groups-one on the north out of East Prussia, the other on the south out of Silesia-had broken through on relatively narrow fronts and were sending armored spearheads on fast drives toward Warsaw and Brst. This was blitzkrieg (lightning war): the use of armor, air power, and mobile infantry in a pincers movement to encircle the enemy.
             Between September 8 and 10, the Germans closed in on Warsaw from the north and south, trapping the Polish forces west of the capital. On September 17, a second, deeper encirclement closed 160 km (100 mi) east, near Brst. On that day, too, the Soviet Red Army lunged across the border. By September 20, practically the whole country was in German or Soviet hands, and only isolated pockets continued to resist. The last to surrender was the fortress at Kock, on October 6.
             In a few weeks of blitzkrieg ("lightning war"), mechanized German divisions overwhelmed the ill-equipped Poles, taking western Poland. The Soviets, not to be outdone, seized the eastern part. Encouraged by success, in 1940 Germany swallowed Denmark, Norway, and the Low Countries and invaded France, which rapidly collapsed. British and French forces were hastily evacuated from Dunkerque to England. Hitler then blockaded Britain with submarines and bombed the country with his new air force. He...