[Illustration: German Confederation of 1815.] Germany did not dare to let Russia mobilize. Had a large Russian army been concentrated in Poland, had Russia been allowed to intrench herself on the Austrian frontier, had she had the opportunity at the beginning of the war to seize the fortress of Thorn and to secure control of the Vistula River, there would have been little to stop the armies of the czar from marching into Berlin. General mobilization by one power, therefore, absolutely compels countermobilization by another power, and unless diplomatic agreements are speedily made and the mobilization checked, it is a prelude to war. The diplomatic interpretations of the discussion over mobilization have been dealt with elsewhere, but it may be summarily said here that Austria was the first of the great powers to begin mobilization in the first part of July, in order to frighten Serbia into submission in the controversy that arose from the assassination of the Austrian Crown Prince at Sarajevo (in Bosnia, Austria) on June 28, 1914. Serbia mobilized, and it was generally believed that this action was due to Serbia's knowledge that Russia was secretly mobilizing. By about July 10, 1914, Germany believed herself satisfied that Russia was actually mobilizing, and she also began secretly to do so. France became suspicious of German military activity, and by the end of the third week and the beginning of the fourth week in July a general, but unadmitted, military preparation was in progress. Actual and admitted mobilization is more or less arbitrarily placed as of August 1, 1914, which date is now generally regarded as the opening of the Great War. In any consideration of Russian mobilization it will be remembered that Russia had three armies, not one, to mobilize, i. e., the armies of European Russia, of the Asiatic Russia, and of the Caucasus. It is also to be remembered that, unlike the German system in which every man has a definite place in a particular corps, the Russian system holds its reserves as reserves solely, and organizes them after they have been gathered together. Slow mobilization is therefore an evil not to be avoided. For this reason one must expect to find Russian mobilization occurring, not on the frontier, but at a point sufficiently far therefrom to be safe from hostile attack during the period of disorganization.