In his 1992 book Ordinary Men, Christopher Browning opposed the theory that Germans in the Nazi era were motivated by the especially virulent anti-Semitism that had characterized German culture for centuries. Analyzing the troops of the special police battalion units, who were the ones who directly killed Jews in the mass raids phase of the Holocaust (prior to the death camps), Browning concluded that these typical middle class workers were not ingrained with anti-Semitism, but rather became killers through peer pressure and indoctrination.