The story
From the novel Nineteen Eighty-Four (1949) by George Orwell, in which the world is divided into the superpowers of Eastasia, Eurasia and Oceania. Oceania is in a state of perpetual war with one of the other powers but its alliance keeps shifting, and the government never acknowledges that its current adversary is its former ally and vice versa.
Etymology from Wiktionary, CC BY-SA 4.0.