"Samuelson is also author (and since 1985 co-author) of an influential principles textbook, Economics, first published in 1948, now in its 19th edition. The book has been translated into forty-one languages and sold over four million copies; it is considered the best-selling economics textbook in history. Written in the shadow of the Great Depression and World War II, it helped to popularize the insights of John Maynard Keynes. A main focus was how to avoid, or at least mitigate, the recurring slumps in economic activity. Samuelson wrote: "It is not too much to say that the widespread creation of dictatorships and the resulting World War II stemmed in no small measure from the world's failure to meet this basic economic problem [the Great Depression] adequately."[16] This reflected the concern of Keynes himself with the economic causes of war and the importance of economic policy in promoting peace.[17]"