cessfully engaged in battle, General von Kluck
adopted the extremely hazardous course of a flank march, across the
front of the Franco-British left wing. Upon receiving intelligence of
this manoeuvre from the Air Service in Paris, General Joffre, seeing
the opportunity of gaining the initiative, ordered an advance to the
attack on September 6, and the First Battle of the Marne, which
resulted from this order, changed the character of the fighting on the
{29} Western Front. The decisive blow was strategical rather than
tactical. It was delivered on a battlefield of 6,000 square miles, and
involved, throughout that area, a struggle of six great armies,
numbering in all 700,000 troops, against a similar number of armies of
at least equal strength. No counter-attack on such a scale had
previously been delivered in any campaign, and the scarcely interrupted
advance of the German armies received a permanent check, while the
strategic aim of the German Staff, namely, the speedy annihilation in
the field of the Franco-British armies, had to be definitely abandoned.

DEVELOPMENT OF THE BATTLE.--The "atmosphere" of battle is thus depicted
in "The Science of War": "When two armies are face to face and one is
superior in numbers to the other, the commander of the smaller army is
confronted by two problems. If the superior army is not yet
concentrated, or is so distributed that the different parts cannot
readily support each other, it may be defeated in detail. If the
superior army is already concentrated, its commander may be induced, by
one means or another, to make detachments, and thus to be weak
everywhere. The first problem is solved by rapidity of manoeuvre,
surprise marches, secrecy, feints to bewilder the adversary in his
concentration, and action on unexpected lines. The second, by skilful
threatening of points for the defence of which the adversary will
detach forces; by concealment of his dispositions; and by drawing the
adversary into terrain where part only of his superior forces can be
employed." "The power of striking 'like a bolt from the blue' is of
the greatest value in war. Surprise was the foundation of almost all
the great strategical combinations of the past, as it will be of those
to come. The first thought and the last of the great general is to
outwit his adversary and to strike where he is least expected. To what
Federal soldier did it occur on the {30} morning of _Chancellorsville_
(May 2-8, 1