[citation needed] At age 21, Nolan began the research that established him as one of England's leading authorities on the American West.
During this time, he also began writing Western fiction as Frederick H. Christian, a pseudonym derived from his own, his wife Heidi's, and his oldest son's first names.
[citation needed] Over the next decade, while working in publishing – with Transworld, then Penguin, Collins, and Granada in London, and later with Ballantine and Warner in New York - he produced 14 Westerns as well as a considerable body of journalism.
On 4 July 1973, Nolan quit his job as a highly paid publishing executive and signed a contract to write eight full-length novels in a year.
One of the foremost authorities on the life and times of Billy the Kid,[3] and the history of the American West in general, Nolan appeared frequently in television documentaries dealing with the subject, as well as lecturing to historical societies in the U.K. and U.s., and on cruise ships.