Therefore, even if he should successfully reach the field of action which he proposed, cross the hills between the two river basins without loss or delay, and be ready to act as he hoped upon the banks of the Danube before the end of June, his stay could not be indefinitely prolonged there, and his every movement would be undertaken under the anxiety which must ever haunt a commander dependent on an insufficient or too distant base of supply. This anxiety, be it noted, would rapidly increase with every march he might have to take southward of the Danube, and with every day’s advance into Bavaria itself, if, as he hoped, the possibility of such an advance should crown his efforts.
We have seen that the great hazard which Marlborough risked made it necessary, as he advanced southward up the Rhine during the first half of his march, to keep Villeroy and Tallard doubtful as to whether his objective was the Moselle or, later, Alsace; and while they were still in suspense, abruptly to leave the valley of the Rhine and make for the crossing of the hills towards the Danube. So long as the French marshals remained uncertain of his intentions, they would not dare to detach any very large body of troops from the Rhine valley to the Elector’s aid: under the conditions of the time, the clever handling of movement and information might create a gap of a week at least between his first divergence from the Rhine and his enemy’s full appreciation that he was heading for the south-east.
He so concealed his information and so ordered his baffling movements as to achieve that end.
So much for the general hazard which would have applied to any commander undertaking such an advance.
But, as I have said, there were two other points peculiar to Marlborough’s political position.
The first was, that he was not wholly free to act, as, for instance, Cæsar in Gaul was free, or Napoleon after 1799. He must perpetually arrange matters, in the first stages with the Dutch commissioner, later with the imperial general, Prince Louis of Baden, who was his equal in command. He must persuade and even trick certain of his allies in all the first steps of the great business; he must accommodate himself to others throughout the whole of it.
Secondly, the direction in which he took himself separated him from the possibility of rapidly communicating his designs, his necessities, his chances, or his perils to what may be called his moral base. This moral base, the seat both of his own Government and of the Dutch (his principal concern), lay, of course, near the North Sea, and under the immediate supervision of England and the Hague. This is a point which the modern reader may be inclined to ridicule until he remembers under what conditions the shortest message, let alone detailed plans and the execution of considerable orders, could alone be performed two hundred years ago. By a few bad roads, across a veritable dissected map of little independent or quasi-independent polities, each with its own frontier and prejudices and independent government, the messenger (often a single messenger) must pass through a space of time equivalent to the passage of a continent to-day, and through risks and difficulties such as would to-day be wholly eliminated by the telegraph. The messenger was further encumbered by every sort of change from town to town, in local opinion, and the opportunities for aid.
More than this, in marching to the Danube, Marlborough was putting between himself and that upon which he morally, and most of all upon which he physically, relied, a barrier of difficult mountain land.
Having mentioned this barrier, it is the place for me to describe the physical conditions of that piece of strategy, and I will beg the reader to pay particular attention to the accompanying map, and to read what follows closely in connection with it.
In all war, strategy considers routes, and routes are determined by obstacles.