On Jan. 27, 1945 the Red Army advancing in Poland arrived in a sleepy town called Oswiecim. Next to it, they found Hell. As they crossed the gates of Auschwitz-Birkenau, they saw discombobulated walking skeletons staring at them with empty eyes. Emaciated corpses were strewn everywhere. The stench of death was overwhelming. More than a million people — mostly Jews — had been murdered there. Auschwitz was the largest and deadliest of the 20,000 concentration camps built by the Germans to create a new world order free of Jews and political dissent.  As the world commemorates International Holocaust Remembrance Day, marking the date of the liberation of Auschwitz, it’s also important to understand and remember what drove the Germans and their helpers in the various countries they invaded to perpetrate the Holocaust. In Nazi Germany, the ancient hatred toward Jews had evolved into something secular and pseudo-scientific. This was something the post-Enlightenment, highly cultured German people could accept as a replacement for the ancient Christian anti-Judaism of their ancestors. By the time Hitler came to power, German anti-Semitism was firmly grounded on the notions that Jews were racially inferior and for being a threat to Christian Germans and everything that was good. Ultimately, any message of hatred that conformed to the conception of Jews established by almost 2,000 years of Christian teachings made sense and was acceptable. Elsewhere in Europe, particularly in the East where the genocide took place and where the Germans found no shortage of auxiliaries for the genocidal duties that took place there, the situation was different. None of the locals who willfully collaborated in the execution of the “final solution of the Jewish question” had been brainwashed by Nazi racial propaganda. In those countries the locals hated Jews for the same reasons other Europeans had hated Jews for centuries: for killing Jesus, for desecrating the host, for poisoning wells, for bringing about the Black Plague, for killing young Christian boys to extract their blood to make Passover bread, for being minions of the devil, for being greedy money-lenders, and any number of other baseless accusations. So, now that the world is paying attention to the consequences of this hatred when looking in through the old electrified fence at Auschwitz-Birkenau, we should not forget where anti-Semitism came from, and recognize that, despite the great progress in Jewish-Christian relations made since the Second Vatican Council, more work needs to be done. — Gabriel Wilensky lives in La Jolla and is the author of “Six Million Crucifixions: How Christian Teachings About Jews Paved the Road to the Holocaust.”