Birnbaum was the youngest son of Nathan Birnbaum, a Jewish philosopher, and Rosa Korngut. Reportedly, his art education consisted of only one month at a Berlin art school in 1913.[1] He served in the Austro-Hungarian Common Army during World War I as a lieutenant in the k.u.k. Feldjäger Battalion No. 17,[2] and was severely injured during the Eleventh Battle of the Isonzo[3][4] where he completely lost one foot, and "shattered" the other;[3] he was confined to a wheelchair thereafter.
Birnbaum survived the Nazi period at first due to the special status conferred to him by his non-Jewish wife (the Nazi concept of geschützte Mischehe, "protected mix-race marriage"; German article here), and then by going into hiding from 1943 until the end of the war in 1945.
References
^Timothy O. Benson et al., Expressionist Utopias, Berkeley, University of California Press, 2001; p. 193.