For three quarters of a century after Monroe's declaration the policy of isolation was more rigidly adhered to than ever, the principal departure from it being the signature and ratification of the Clayton-Bulwer Treaty in 1850. By the terms of this treaty we recognized a joint British interest in any canal that might be built through the isthmus connecting North and South America, undertook to establish the general neutralization of such canal, and agreed to invite other powers, European and American, to unite in protecting the same. Owing to differences that soon arose between the United States and England as to the interpretation of the treaty, the clause providing for the adherence of other powers was never carried out. For nearly a hundred years we have successfully upheld the Monroe Doctrine without a resort to force. The policy has never been favorably regarded by the powers of continental Europe. Bismarck described it as "an international impertinence." In recent years it has stirred up rather intense opposition in certain parts of Latin America. Until recently no American writers appear to have considered the real nature of the sanction on which the doctrine rested. How is it that without an army and until recent years without a navy of any size we have been able to uphold a policy which has been described as an impertinence to Latin America and a standing defiance to Europe? Americans generally seem to think that the Monroe Doctrine has in it an inherent sanctity which prevents other nations from violating it. In view of the general disregard of sanctities, inherent or acquired, during the early stages of the late war, this explanation will not hold good and some other must be sought. Americans have been so little concerned with international affairs that they have failed to see any connection between the Monroe Doctrine and the balance of power in Europe. The existence of a European balance of power is the only explanation of our having been able to uphold the Monroe Doctrine for so long a time without a resort to force. Some one or more of the European powers would long ago have stepped in and called our bluff, that is, forced us to repudiate the Monroe Doctrine or fight for it, had it not been for the well-grounded fear that as soon as they became engaged with us some other European power would attack them in the rear. A few illustrations will be sufficient to establish this thesis.