Lord Liverpool and Liberal Toryism 1820 to 1827 (Cambridge: Cambridge University Press, 1941; 2nd edn, Hamden, CT: Archon, 1967)
Britain and the Dominions (Cambridge: Cambridge University Press, 1951)
The Effect of the Loss of the
American Colonies upon British Policy (London: Historical Association, 1957; 2nd edn, 1966)
The Character of American History, Aids for Teachers, vol. 3 (London: Macmillan, 1960; 2nd edn, 1965)
An American Crisis: Congress and Reconstruction, 1865–1867 (New York: St Martin's Press, 1963)
The Evolution of American Democracy (New York: Dial Press, 1970)
Conflict and Transformation in the U.S., 1844-1877 (Baltimore, MD: Penguin, 1973)
The United States, 1789-1890: Sources of History (Ithaca, NY: Cornell University Press, 1975)
Parties and Political Conscience (Millwood, NY: KTO Press, 1979)
Scotus Americanus: A Survey of the Sources for Links Between Scotland and America in the Eighteenth Century (Edinburgh: Edinburgh University Press, 1981)
Investigation and Responsibility: Public Responsibility in the United States, 1865–1900 (Cambridge: Cambridge University Press, 1984)
Welfare, Democracy, and the New Deal (Cambridge: Cambridge University Press, 1988)
(with P. M. H. Cooper) Selwyn College: A History (Durham: Pentland Press, 1994)