During the half century that intervened between John Quincy Adams and James G. Blaine, the Monroe Doctrine, it was commonly believed, had prevented the expansion of the territories of European powers in the Americas. It had also relieved the United States both of the necessity of continual preparation for war and of that constant tension in which the perpetual shifting of the European balance of power held the nations of that continent. But the Monroe Doctrine was not solely responsible for these results. Had it not been for the British Navy, the United States would in vain have proclaimed its disapproval of encroachment. Nor, had Europe continued united, could the United States have withstood European influence; but Canning's policy had practically destroyed Metternich's dream of unity maintained by intervention, and in 1848 that whole structure went hopelessly tumbling before a new order. Yet British policy, too, failed of full realization, for British statesmen always dreamed of an even balance in continental Europe which Great Britain could incline to her wishes, whereas it usually proved necessary, in order to preserve a balance at all, for her to join one side or the other. Divided Europe therefore stood opposite united America, and our inferior strength was enhanced by an advantageous position. The insecurity of the American position was revealed during the Civil War. When the United States divided within, the strength of the nation vanished. The hitherto suppressed desires of European nations at once manifested themselves. Spain, never satisfied that her American empire was really lost, at once leaped to take advantage of the change. On a trumped up invitation of some of the inhabitants of Santo Domingo, she invaded the formerly Spanish portion of the island and she began war with Peru in the hope of acquiring at least some of the Pacific islands belonging to that state. More formidable were the plans of Napoleon III, for the French, too, remembered the glowing promise of their earlier American dominions. They had not forgotten that the inhabitants of the Americas as far north as the southern borders of the United States were of Latin blood, at least so far as they were of European origin. In Montevideo there was a French colony, and during the forties France had been active in proffering her advice in South American disputes. When the second French Republic had been proclaimed in 1848, one of the French ministers in South America saw a golden chance for his country to assume the leadership of all Latin America, which was at that time suspicious of the designs of the United States and alarmed by its rapid expansion at the expense of Mexico. With the power of the American Government neutralized in 1861, and with the British Navy immobilized by the necessity of French friendship, which the "Balance" made just then of paramount interest to Great Britain, Napoleon III determined to establish in Mexico an empire under French influence.