"When I was a boy in the Midwest during the early 1950s, we used to play games emulating the heroics of our soldiers during the Second World War," he began.
But all the time, young Zwick felt a gnawing sense of shame that Europe's Jews, according to all accounts of the time, had gone to their deaths meekly, without fighting back.
But once he read the amazing story of the Bielski brothers, who not only fought the Nazis, but also struggled with hostile local populations and anti-Semitic Soviet troops, Zwick gradually discovered that there were hundreds of similar reports on Jewish resistance fighters.
"My greatest hope for the film is that another 15-year-old boy in the Midwest will see it and will never feel the shame I did," Zwick concluded.
After the screening, Zwick, national ADL director Abe Foxman, and the audience engaged in a lively discussion on the film's impact.
Foxman brought a special perspective to the discussion as a child Holocaust survivor who had actually known two of the Bielski brothers.
For the first time, he said, the film reveals the truth about the collaboration of many Lithuanians, Poles and Ukrainians with the Nazi conquerors, and exposes the pervasive anti-Semitism among Soviet soldiers.
Surprisingly, Foxman was unsure how "Defiance" will be received by Jewish viewers. "I am not certain whether we are ready to embrace fighting Jews," he declared.
But judging by the audience applause and comments, Foxman's fears may well be unfounded.