Beginning in the 1960s and early 1970s he published on American economic history in the 19th century, including The Jacksonian Economy (1969) and Causal Factors in American Economic Growth in the Nineteenth Century (1975), as well as Reckoning with Slavery (1976), which was an examination of the slave economy and its effects.
The conclusions of his 1971 paper on Central Banks and Economic and Social Welfare programs foreshadowed what is probably his most influential and best known work: Did Monetary Forces Cause the Great Depression?
[citation needed] He would later revisit this thesis in his 1989 work Lessons from the Great Depression, as well as publish several papers building on his conclusions.
He joined, in some way, the conclusions of Keynes and Friedman: the Great Depression started with troubles in the 'real economy' later expanded to the financial world via speculation and money destruction (also see the analysis of Rondo Cameron about 'wildcat banking').
His 1987 empirical survey of AT&T, entitled The Fall of the Bell System has affected how new entrepreneurial businesses are viewed.