His pleasant life in the middle-class family was interrupted in 1941, when Ustaše took the power with the Independent State of Croatia establishment.

His father was forced to retire from his job position and was sent to concentration camp, but with the help of Vladko Maček he was released.

He was rescued from the deportation to Nazi concentration camps by physician Miroslav Schlesinger, who organized the departure of the Croatian Jewish doctors to Bosnia, to combat endemic syphilis in 1941.

[6][7] 80 Jewish doctors were sent to Bosnia by Independent State of Croatia authorities, among them Steiner and his wife Zora Goldschmidt-Steiner, one of the most prominent surgeons in the war.

[5] Steiner meet Josip Broz Tito during the preparation for the second session of the Anti-Fascist Council of the People's Liberation of Yugoslavia in Jajce.

The last 25 years of his life, Steiner volunteered at a Jewish retirement home Lavoslav Schwarz in Zagreb.