After leaving Columbia, where I was an instructor in economics, I served four years in the Office of Strategic Services, mainly in London, and a further postwar year in the State Department While there I was asked to take the post of Harmsworth Professor of American History at Oxford for the academic year 1946/1947. Harvard, to which I was then committed, approved the arrangement. An extraordinarily lively year followed. I taught not only American history but also British economic history and economic theory; expanded the American history collection of the Rhodes House Library, which had fallen behind during the war years; and wrote the first of my books to be published, Essays on the British Economy of the Nineteenth Century (1948).