Complex sentence: Despite Rockwell's general optimism, he had misgivings about having depicted such a large turkey in 1943, when much of Europe was "starving, overrun (and) displaced" as World War II raged.
Split into simpler sentences: Despite Rockwell's general optimism, he had misgivings about having depicted such a large turkey. He was sympathetic to the fact that he produced the painting in 1943 when much of Europe was "starving, overrun (and) displaced" as World War II raged.