He was born in 1893 in the New York brownstone house near
Washington Square where he lived all his adult life, a member of Edith
Wharton's settled, circumscribed world of ordered privilege whose
affluent, well-travelled, and sophisticated men and women traced their
lineage back to the Founding Fathers and their principles to the American
Revolution. His father was an artist who served as Consul General to
Italy, and Armstrong was brought up in a milieu which took for granted
the fact that there existed a world outside the United States. He died in
1973, as the United States finally withdrew from the Vietnam War, a
conflict which deeply distressed him and shattered the foreign policy elite
and its controlling consensus, whose creation had been a major part of his
life's work. In an obituary notice Arthur M. Schlesinger, Jr., described
him as “a New York gentleman of a vanishing school,” who “treated
every one, old or young, famous or unknown, with the same generous
courtesy and concern.”