The Defenders is a 1953 science fiction novelette by American author Philip K. Dick, and the basis for Dick's 1964 novel The Penultimate Truth. It is one of several of his stories to be expanded into a novel. The story was first published in the January 1953 issue of Galaxy Science Fiction. In 1956, the story was adapted for the radio program X Minus One by George Lefferts. Eight years ago a nuclear war began between the United States and the Soviet Union. American survivors evacuated to gigantic bunkers miles under ground. Sophisticated, radioactivity-immune robots called "leadys" continue fighting the war on the devastated surface that is far too dangerous for humans. The Soviets have similarly evacuated underground, and each side builds powerful weapons and vehicles for the remote-controlled war they only see from film that the robots deliver. The security department asks Taylor, an American war planner, to observe the interrogation of a leady regarding the progress of the war. Although the robot reports that lethal radioactivity and sophisticated new Soviet weapons continue to make the surface dangerous for humans, the observers find that the leady is not radioactive. Taylor learns that this is the second such robot the security department has found; it assigns him to an expedition, wearing lead suits, to investigate the truth about surface conditions. Taylor's group surprises the leadys at the surface and demands to see the outside. Although the robots attempt to delay the humans as long as possible, the group discovers outside the bunker an undamaged valley with forests, animals, and a farm. The leadys reveal that the war ended as soon as the humans evacuated because the robots could not see a rational purpose for it. Analyzing history, they found that groups of humans warred with each other until they matured to overcome conflict. Humanity is almost ready for a single culture, the current worldwide division into American and Soviet sides being the final step.