The Wealth and Poverty of Nations: Why Some Are So Rich and Some So Poor (W W Norton & Company; 1998)

... the causes of the wealth and poverty of nations—the grand object

of all enquiries in Political Economy.

—Malthus to Ricardo, letter of 26 January 1817*

• J. M. Keynes, Collected Works, X, 97-98, quoted in Skidelsky, John Maynard Keynes:
  The Economist as Saviour 1920-1937, p. 419. My thanks for this quotation to Morton
  Keller.