McClellan's advance upon Richmond, in its beginnings at least, antedated the great conflict at Shiloh. But its crisis did not come until much later, nor did it in its early progress involve aught that was of significance in its bearing upon the conduct and outcome of the war.
It seems proper therefore to discuss Shiloh and other operations in the Mississippi Valley first, leaving the campaign in Virginia for later consideration.
The Confederates, before the fall of Fort Donelson and Fort Henry, were maintaining a line of offensive defense in Kentucky. This line extended from the Big Sandy in the eastern part of the state to Columbus on the Mississippi river in the extreme west.
The line was in many respects defective. The Confederate center of operations was at Bowling Green, while the two ends of the defensive line lay much farther north than that. The line thus constituted what in military parlance is known as a reëntering angle. The enemy pushing into such an angle with forces greater than those that defended it or even with an inferior force, had easy choice to attack on either side as he pleased, concentrating at will, while compelling the Confederates to scatter their forces along the whole of an extensive line by way of defending all parts of it equally.
It was the original purpose of those who devised this defensive system to correct the fault by pushing their center forward from Bowling Green to Paducah on the Ohio river, nearly fifty miles above the mouth of that stream. Had this been accomplished, it would have made the angle of defense a salient instead of a reëntering one.
Let us explain the advantage of this for the benefit of the non-military reader. If the Confederates could have established themselves at Paducah with their lines trending off to the southeast on the one side and to the southwest on the other, they, instead of their enemies, would have had choice of positions in which to concentrate. Assailed at any point it would have been easy for them to throw all possible force quickly to the defense of the threatened position.
Grant interfered with all this planning when he moved up the Ohio, and seized upon Paducah, which was quickly fortified so strongly as to render the execution of the scheme thereafter impracticable. From that time forward it was clear that the Confederates must either maintain their line of defense by means of a vast and dangerously unmanageable reëntering angle, or they must withdraw from their two advanced wing points. To do this latter thing would have been to abandon Kentucky completely, and it was no part of the Confederate program to do that.
A second defect in this scheme of defense was that the line thus formed was traversed by two rivers, the Tennessee and the Cumberland, both practically navigable by steamboats. It was obvious to ordinary common-sense that should both or either of these rivers at any time fall under control of the enemy, with his multitudinous gunboats and other river craft which could easily be made to carry guns, the western half of the Confederate force must be completely and at once cut off from all but a very roundabout and slow communication with its allies on the east.
Here was a danger which must have presented itself obtrusively to the minds of those who formed and ordered this military arrangement. It is difficult for a military critic in this later day to understand or to conceive upon what principle of scientific warfare such a line was accepted as even tolerably judicious. Its adoption seems in fact to have been determined more by political than by military considerations.
In order to meet the difficulty the Confederates created the two great fortresses—Henry and Donelson—to defend the rivers. These forts were curiously misplaced. They were located one upon the one river, and the other upon the other, at a point near the dividing line between Kentucky and Tennessee. At that point the two rivers run within eleven miles of each other. But a little farther down the streams—that is to say a little farther north—their course brings them within three miles of each other. Here obviously on all accounts was the point at which the defensive works should have been constructed. In that case the two forts would have been within easy supporting distance of each other and neither could have been assailed from the rear. Moreover, we have the authority of no less eminent an engineer than General Beauregard for saying that the ground at this point is well fitted by its natural conformation for purposes of defense, while at the point actually selected for the two fortresses it is peculiarly lacking in that advantage. But the more defensible position was in Kentucky and purely political considerations had weight in determining the choice of the less advantageous point of defense in Tennessee.