Even though the argument runs counter to much of the detailed scholarship on the subject, Britain's decision in 1921 to terminate its alliance with Japan is sometimes held in general historical surveys to be a major blunder that helped to pave the way to the Pacific War. The lingering sympathy for the combination with Japan is largely due to an historical myth which has presented the alliance as a particularly close partnership. The roots of the myth lie in the inter-war period when, in order to attack the trend towards internationalism, the political right in Britain manipulated memory of the alliance so that it became an exemplar of ‘old diplomacy’. It was then reinforced after 1945 by post-war memoirs and the ‘declinist’ literature of the 1960s and 1970s. By analysing the origins of this benevolent interpretation of the alliance, this article reveals how quickly and pervasively political discourse can turn history into myth and how the development of myths tells us much about the time in which they were created.