Between these two methods of attack there is, as a rule, this difference. By striking at the centre of the enemy's line, his army can be separated into two parts, and then be defeated in detail. In this case the aim is so to manoeuvre as to outnumber the enemy on the battle-field. But by striking at the flank, the enemy is often given the opportunity of concentrating his forces. Even if one flank is defeated, it can fall back upon the other, and perhaps even then make a successful stand against the attacking army. In this case the advantages generally aimed at are to threaten or sever the communications of the enemy, and to force him to fight a battle where a defeat will ruin his army. From the foregoing, it is evident that these two methods of attack have a tendency to produce opposite results. A direct attack upon the enemy, if successful, breaks up and scatters his forces. On the other hand, a flank attack gives him a chance to concentrate, but at the same time places him in a position where a defeat will ruin him. In making a choice between these two methods of attack, the able general will be guided in great measure by the positions occupied by the enemy's forces. But, as a rule, if he adopt one method, he must abandon the advantages to be derived from the other. Thus, should he decide to attack the centre of the enemy's line, he may reasonably expect to divide the forces of the enemy, and afterwards to defeat them in detail; but he cannot expect to threaten at the same time their communications, and cut them from their base of operations. On the other hand, if he make a flank attack, he may reasonably expect to sever the communications of the enemy, and thus force him to fight a battle under disadvantageous circumstances; but he cannot expect to defeat in turn the several parts of the enemy's army. But in the campaign between Moreau and Kray, it is a remarkable fact that the positions of the Austrian forces were such that the advantages of both a front and flank attack could be obtained by the French. By crossing the Rhine at Schaffhausen, and by attacking the flank of Kray in the Black Forest, the French would not only separate the Austrian left from the Austrian centre and right, but would threaten the Austrian communications with Ulm. From the beginning Bonaparte saw clearly this fact. His eye took in the entire situation. Thus it was that he was anxious to have Moreau undertake this movement. Thus it was that he himself had thought seriously at one time of uniting the Army of Reserve with the Army of the Rhine, and of moving against the left flank of Kray's forces in the Black Forest.