Holocaust trains were railway transports run by the "" national railway system under the strict supervision of the German Nazis and their allies, for the purpose of forcible deportation of the Jews, as well as other victims of the Holocaust, to the German Nazi concentration, forced labour, and extermination camps.
The Catholic Church in Poland was brutally suppressed by the Nazis during the German Occupation of Poland (1939-1945).
 Repression of the Church was at its most severe in Polish areas annexed by Nazi Germany, where churches were systematically closed and most priests were either killed, imprisoned, or deported.
 From across Poland, thousands of priests died in prisons and concentration camps; thousands of churches and monasteries were confiscated, closed or destroyed; and priceless works of religious art and sacred objects were lost forever.
 Church leaders were targeted as part of an overall effort to destroy Polish culture.
 At least 1811 Polish clergy died in Nazi concentration camps.
 An estimated 3000 clergy were killed in all.
 Hitler's plans for the Germanization of the East saw no place for the Christian Churches.
Maria Mandl (also spelled Mandel; 10 January 1912 – 24 January 1948) was an Austrian "SS-Helferin" infamous for her key role in the Holocaust as a top-ranking official at the Auschwitz-Birkenau extermination camp where she is believed to have been directly complicit in the deaths of over 500,000 female prisoners.
The Holocaust in German-occupied Poland was the last and the most lethal phase of the Nazi "Final Solution of the Jewish Question" ("Endlösung der Judenfrage") marked by the construction of death camps on German-occupied Polish soil.
 The genocide officially sanctioned and executed by the Third Reich during World War II, collectively known as the Holocaust, took the lives of more than three million Polish Jews.
 The extermination camps played a central role in the implementation of the German policy of systematic and mostly successful destruction of over 90% of the Polish-Jewish population of the Second Polish Republic.
The Białystok Ghetto (Polish: "getto w Białymstoku" ) was a World War II Jewish ghetto set up by Nazi Germany between July 26 and early August 1941 in the newly formed "Bezirk Bialystok" district of the Third Reich within Nazi occupied Poland.
 About 50,000 Jews from the vicinity of Białystok and the surrounding region were herded into a small area of the city, which was turned into the "Bezirk's" capital.
 The ghetto was split in two by the Biała River running through it "(see map)".
 Most inmates were put to work in the forced-labor enterprises for the German war effort, primarily in large textile, shoe and chemical companies operating inside and outside its boundaries.
 The ghetto was liquidated in November 1943 after the Białystok Ghetto uprising was crushed.
 All its inhabitants were either killed locally, or transported in Holocaust trains to the Majdanek and Treblinka extermination camps.
The General Government (German: "Generalgouvernement" , Polish: "Generalne Gubernatorstwo" , Ukrainian: Генеральна губернія ), also referred to as the General Governorate, was a German zone of occupation established after the joint invasion of Poland by Nazi Germany and the Soviet Union in 1939 at the onset of World War II.
 The newly occupied Second Polish Republic was split into three zones: the General Government in its centre, Polish areas annexed by Nazi Germany in the west, and Polish areas annexed by the Soviet Union in the east.
 The territory was expanded substantially in 1941 to include the new District of Galicia.
Auschwitz concentration camp (German: "Konzentrationslager Auschwitz" , ] , also "KZ Auschwitz " or "KL Auschwitz ") was a network of German Nazi concentration camps and extermination camps built and operated by the Third Reich in Polish areas annexed by Nazi Germany during World War II.
 It consisted of (the original camp), Auschwitz II–Birkenau (a combination concentration/extermination camp), (a labor camp to staff an IG Farben factory), and 45 satellite camps.
This article presents a partial list of the most prominent Nazi German concentration camps set up across Europe during the course of World War II and the ensuing Holocaust.
 A more complete list drawn up in 1967 by the German Ministry of Justice names about 1,200 camps and subcamps in countries occupied by Germany, while the Jewish Virtual Library writes: "It is estimated that the Germans established 15,000 camps in the occupied countries."
 The concentration camps are not to be confused with the extermination camps which were designed and built exclusively to kill prisoners on a massive scale immediately upon arrival.
 The extermination camps of Operation Reinhard such as Belzec, Sobibór and Treblinka served as "death factories" in which German SS and police murdered nearly 2,700,000 Jews either by asphyxiation with poison gas or by shooting.
 Meanwhile, the concentration camps listed herein served primarily as detention and slave labor exploitation centers.
 Most of them were destroyed by the Germans in an attempt to hide the evidence of war crimes and crimes against humanity; nevertheless tens of thousands of prisoners sent on death marches were liberated by the Allies afterward.
Below is the list of subcamps of Gross-Rosen "Stammlager" complex of Nazi concentration camps built and operated by Nazi Germany during World War II.
 The camps are arranged alphabetically by their Nazi German designation.
 For the list of present-day locations in alphabetical order, please use table-sort buttons.
Death marches (Todesmärsche in German) refer to the forcible movements of prisoners in Nazi Germany.
 They occurred at various points during the Holocaust, including in 1939 in the Lublin province of Poland, in 1942 in Ukraine, and between Autumn 1944 and late April 1945 from Nazi concentration camps and prisoner of war camps near the front, to camps inside Germany away from front lines and Allied forces to remove evidence from concentration camps and to prevent the repatriation of prisoners of war.

Question: Maria Mandl, was an Austrian "SS-Helferin" infamous for her key role in the Holocaust as a top-ranking official at the Auschwitz-Birkenau, it was a network of German Nazi concentration camps and extermination camps built and operated by the Third Reich in Polish areas annexed by Nazi Germany during which historic event?
Answer: World War II