Strategy prepares for battles; tactics fights them.
The tactics of any battle must be in the hands of the commanders-in-chief on both sides.

Any other arrangement is inconceivable; but the strategy controlling the series of battles in any war cannot now be committed to them solely; though it was usually committed to them until lately.

In the days when Alexander went to war, or even when Napoleon and Nelson went to war, twenty-one centuries later, no telegraph by sea and land made swift communication possible; and the commanders on the spot were the only ones in possession of enough information about the contending forces to decide what measures should be taken.

Even in those days, however, the capitals of the countries engaged in war, by reason of their knowledge of what was passing in the way of policy, exerted an influence on the strategy of the forces on both sea and land; Caesar, for instance, was embarrassed in many of his operations by the Roman Senate, and it was for this reason that he crossed the Rubicon and passed from Gaul into Italy.

When William I and Napoleon III went to war in 1870, however, Von Moltke had foreseen the effects of the telegraph and of rapid-mail communications, in giving to the headquarters of the army information of a much greater scope and reliability than had previously been the case, and had established a General Staff which had elaborated plans whereby not only would the commanders-in-chief in the field have the assistance of information compiled at headquarters, but whereby the general nature of the operations of a war, especially those operations at the outset on which the future conduct of the war would largely depend, would be decided and laid down in advance and during times of peace.