Second Variety was a short story written in 1953. (But there is also a collection of short stories called Second Variety, published in 1981).
The science fiction story is set in the aftermath of nuclear war between the Soviet Union and the United Nations, where the only inhabitants are killer robots.
Humanity is central to the story; Dick explores questions such as, how can we really know who is human and who is not and has mechanization caused people to feel alienated? Dick is also interested in the constantly evolving relationship between man and machine.