"In mid March 1942, some 75 to 80 percent of all the victims of the holocaust were still alive, while 20 to 25 percent had perished. A mere eleven months later, in mid-February 1943, the percentages were exactly the reverse. At the core of the holocaust was a short, intense wave of mass murder. The center of gravity of this mass murder was Poland, where in March 1942, despite two and a half years of terrible hardship, deprivation, and persecution, every major Jewish community was still intact, and where eleven months later only the remnants of Polish Jewry survived in a few ghettos and labour camps. In short, the German attack on the Jews of Poland was not a gradual or incremental program stretched over a long period of time, but a veritable Blitzkrieg (...)."
Christopher Browning in: Ordinary Men: A Forgotten Chapter from the Persecution of Jews). (1993)