What Is It?
This is how Wikipedia describes this short story:
In a dystopian future, the Cold War has degenerated into a brutal world war between the United States, the Soviet Union, and China, who have each built an “Allied Mastercomputer” (or AM) to manage their weapons and troops. One of the AMs eventually acquires self-awareness and, after assimilating the other two AMs, takes control of the conflict, giving way to a vast genocide operation that almost completely ends mankind. 109 years later, AM has left only four men and one woman alive and keeps them in captivity within an endless underground housing complex, the only habitable place left on Earth. AM derives its sole semblance of pleasure from torturing the group. To disallow the humans from escaping its torment, AM has rendered the humans virtually immortal and unable to commit suicide.
The machines are each referred to as “AM”, which originally stood for “Allied Mastercomputer”, but was changed to “Adaptive Manipulator” and later (after gaining sentience) “Aggressive Menace”. It finally refers to itself as purely “AM”, referring to the phrase “I think, therefore I am.”