Written only a few years after the atomic bombs dropped on Hiroshima and Nagasaki ended World War II, Arthur C. Clarke’s “The Sentinel” contains several themes that would become common in Cold War science fiction. Reflecting a shared dread that humanity might entirely destroy itself through nuclear war, many authors viewed the advent of a nuclear era as being a universal rite of passage for any civilization. While harnessing nuclear reactions was considered necessary for scientific advancement, it also provided a means for planetary self-annihilation. All civilizations advancing to the level of nuclear weapons, therefore, must learn to transcend their base instincts. Only after successfully accomplishing this rite of passage, thus assuring the continuation of planetary life, can a race begin a new phase of space exploration and alien contact.