This is a study of power. More particularly, it is a study of how power has been lost and won in international politics, of how Great Britain, the greatest of the great Powers in 1930, came to surrender its pre-eminence to the United States by the end of the Second World War. In this context, it shows how British leaders responded to the American question in their diplomacy; and why the British side of this relationship evolved as it did. What constitutes ‘power’ is a vexed question. Political scientists have devised theoretical models to find an answer; but in the recent words of one of them: ‘Even if they were substantially correct, these statements would not be very satisfying, if only because all forms of guessing are not equally imprecise.’ For thirty years, international historians have embarked on the same crusade, particularly American ‘revisionists’, whose explanations for their country's advent as the world's leading Power have touched its logical corollary – Britain's enfeeblement. Concentrating on the crude connexion between wealth and national potency, they have been joined lately by Paul Kennedy, who provides the apotheosis of economic determinism respecting Britain and the United States. ‘Austria-Hungary was gone, Russia in revolution, Germany defeated,’ he observes about the situation after the First World War; ‘yet France, Italy, and even Britain itself had also suffered heavily in their victory.’