We shall be gratified when the Emperor shall give to us ... definite information of the time when French military operations may be expected to cease in Mexico.
Napoleon finally decided that, in view of the European situation, he could not risk a war with the United States, and in the issue of April 5, 1866, the _Moniteur_ announced that the Emperor had decided that the French troops should evacuate Mexico in three detachments: the first to leave in November, 1866; the second in March, 1867; and the third in November, 1867. In the course of a conversation with Mr. Bigelow the day following M. Drouyn de Lhuys acknowledged that this statement was official.[236] The decision of the emperor was officially made known to the United States in a note of April 21, 1866. Seward had very fortunately left a loophole in his dispatch of February 12, in the statement that the United States would continue to pursue its policy of neutrality after the French evacuation. De Lhuys said:
We receive this assurance with entire confidence and we find therein a sufficient guarantee not any longer to delay the adoption of measures intended to prepare for the return of our army.[237]
American historians have usually attributed Napoleon's backdown to Seward's diplomacy supported by the military power of the United States, which was, of course, greater then than at any other time in our history. All this undoubtedly had its effect on Napoleon's mind, but it appears that conditions in Europe just at that particular moment had an even greater influence in causing him to abandon his Mexican scheme. Within a few days of the receipt of Seward's ultimatum Napoleon was informed of Bismarck's determination to force a war with Austria over the Schleswig-Holstein controversy. Napoleon realized that the territorial aggrandizement of Prussia, without any corresponding gains by France, would be a serious blow to his prestige and in fact endanger his throne. He at once entered upon a long and hazardous diplomatic game in which Bismarck outplayed him and eventually forced him into war. In order to have a free hand to meet the European situation he decided to yield to the American demands.
About the time that the French government announced its intention of withdrawing its forces from Mexico, it was found that troops were being enlisted in Austria for the Mexican "foreign legion." The United States government at once took measures to prevent the French troops from being replaced by Austrians by declaring to the Austrian government through Mr. Motley, "that in the event of hostilities being carried on hereafter in Mexico by Austrian subjects, under the command or with the sanction of the government of Vienna, the United States will feel themselves at liberty to regard those hostilities as constituting a state of war by Austria against the republic of Mexico; and in regard to such war, waged at this time and under existing circumstances, the United States could not engage to remain as silent and neutral spectators."[238]