It’s a bitter paradox that even the most virulently antiwar of the famous soldier poets of World War I felt the lure of battle. “He was not eager to die,” Michael Korda writes of Siegfried Sassoon in his new book, “Muse of Fire,” “but he yearned for the excitement and camaraderie of combat.” An acting captain, Sassoon regarded his troops as “his family, his children,” Korda writes. “Despite the nagging guilt that he was going to lead many of them to their deaths, he was happy.”