The tiny fictional Duchy of Grand Fenwick is central to the 1959 film 'The Mouse that...' what?

'The Mouse That Roared' is a 1955 Cold War satirical novel by Irish American writer Leonard Wibberley, which launched a series of satirical books about an imaginary country in Europe called the Duchy of Grand Fenwick. Wibberley went beyond the merely comic, using the premise to make commentaries about modern politics and world situations, including the nuclear arms race, nuclear weapons in general, and the politics of the United States.

The novel originally appeared as a six-part serial in the Saturday Evening Post from December 25, 1954 through January 29, 1955, under the title 'The Day New York Was Invaded'. It was published as a book in February 1955 by Little, Brown. The British edition used the author's original intended title, 'The Wrath of Grapes', a play on John Steinbeck's 'The Grapes of Wrath'.

Wibberley wrote one prequel (1958's 'Beware of the Mouse') and three sequels: 'The Mouse on the Moon' (1962), 'The Mouse on Wall Street' (1969), and 'The Mouse that Saved the West' (1981). Each placed the tiny Duchy of Grand Fenwick in a series of absurd situations in which it faced superpowers and won.