In 1941, a new law required all Jews living in Hungary to prove that their family had lived in and paid taxes in Hungary back to 1851. Halberstam, his wife, and their eleven children were arrested and brought to
Budapest, where the family was separated. He was jailed with a group of leaders who were later sent to
Auschwitz, but he was released and the family returned to Kolozsvár. On 19 March 1944, the Germans invaded Hungary and Hungarian Jews were
confined to ghettos and then deported to the Auschwitz death camp. The Klausenburg ghetto was established on 1 May 1944, and was liquidated via six transports to Auschwitz between late May and early June. Halberstam fled to the town of
Nagybánya, where he was conscripted into a
forced-labor camp along with 5,000 other Hungarian Jews. About a month after his arrival the Nazis took over Hungary. He was sent to Auschwitz, where his wife and nine of their children who remained with her in Klausenburg had been sent several months earlier. They did not survive. Halberstam was assigned to a work unit in the
Warsaw Ghetto and later was sent to the
Dachau concentration camp as a slave laborer, and then to the Muldorf Forest, where the Nazis were building an underground airport and missile batteries. In the spring of 1945 the Germans disbanded the Muldorf camp and sent the inmates on a
death march from which the survivors, including Halberstam, were liberated by Allied troops in late April. Halberstam's wife and ten of his children were murdered by the Nazis during World War II. His eldest son survived the war but died of illness in a refugee camp soon after. After Allied liberation, the Klausenberger Rebbe met
Dwight D. Eisenhower and criticized Allied failure to bomb the death camps and train tracks leading to them, insisting it could have saved millions of Jewish lives. In spring 1946 he went to the United States, where he established his court in the
Williamsburg section of
Brooklyn, New York, in 1947. ==Remarriage==