He was a prolific historical author, best known for his abridgement (still in print) of Arnold J. Toynbee's A Study of History.
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Isbell was promoted to Captain in 1942 while in command of the Naval Air Station, Sitka, Alaska.
Toynbee was the uncle, via his brother Harry Valpy Toynbee, of universal historian Arnold Joseph Toynbee (1889–1975); with whom he is often confused.
Born into a long-established Bedfordshire family, he was educated at Winchester College, a contemporary of Arnold J. Toynbee and R.M.Y. Gleadowe, and at New College, Oxford, which he left with a First in Classical Moderations in 1911.
A Study of History, a 12-volume book by British historian Arnold J. Toynbee, finished in 1961