In P. D. James's dystopian novel The Children of Men, what global crisis has made humanity infertile?

In P. D. James's dystopian novel The Children of Men, mass human infertility has brought reproduction to a halt.

The story is set in England in 2021, after the world's last generation of children has grown old and no new babies have been born. The crisis affects both men and women, although the novel's opening explanation emphasizes widespread male sterility. Society responds with political control, medical investigations, and growing despair.

This premise is sometimes confused with a pandemic or a conventional population collapse caused by war. The defining catastrophe in the novel is infertility, not mass death from an identified infectious disease. James leaves the biological cause unresolved, which keeps the focus on political and moral consequences rather than on a scientific cure.

The novel was published in 1992 under the title The Children of Men. Alfonso Cuarón's 2006 film adaptation changes many plot details and presents a different political and visual world, so facts from the film should not automatically be attributed to James's book.