You could argue that they are all theater of war, the movies, Hollywood and otherwise set in World War II Europe: the fable, “Boy in the Striped Pajamas,” the action thriller “Defiance,” even the irresponsible and insulting “Valkyrie,” and the ones that look at the period after: the emotionally resonant “The Reader” and “Adam Resurrected” with its disturbing depiction of a comic who survived the concentration camps as a Nazi commando's pet dog (Jeff Goldblum in an elastic Gumby defying role). But the title “Theater of War,” about the making of the 2006 Public Theater production of “Mother Courage and her Children” in Central Park, from the Brecht play adapted by Tony Kushner and starring Meryl Streep, belongs to a fine documentary now showing at Film Forum. This movie says much about the war era providing excellent footage on Brecht's exile to the United States and his interview before the House Unamerican Committee. Set several centuries before, during the time of the Thirty Years War, “Mother Courage” brilliantly illustrates paradoxically how man's motivation toward the commerce of war is also our greatest downfall. Interviewed for “Theater of War,” Meryl Streep whose performance as Mother Courage showed the world she could sing (before “Mamma Mia!”), said it's all in the mouth of the mother, any mother, seeing her dead child, crying, “Why?”