was, I believe,
almost impossible for the Germans to send troops to Transylvania, which
accounts for the rapidity of the Rumanian advance at the beginning of
their operations. The fallacy in the Allied reasoning seems to me to
have been that every one overlooked certain vital factors in the German
situation. First, that she would ultimately support any threat against
Hungary to the limit of her capacity, even if she had to evacuate
Belgium to get troops for this purpose. For with Hungary out of the war
it is a mate in five moves for the Central Empires. Second: the Allies
failed to analyze correctly the troop situation on the eastern front,
apparently failing to grasp one vital point. An army can defend itself
in winter, with the heavy cold and snows of Russia sweeping the barren
spaces, with perhaps sixty per cent of the number of troops required to
hold those identical lines in summer. It should have been obvious that,
when the cold weather set in in the north, the Germans would take
advantage of this situation, and by going on the defensive in the north
release the margin representing the difference in men required to hold
their lines in summer and in winter. Possibly the same condition applies
to the west, though I cannot speak with any authority on that subject.
Apparently this obvious action of the Germans is exactly what happened.
When their northern front had been combed, we find forces subtracted
piecemeal from the north, reaching an aggregate of thirty divisions, or
at least nearly fifteen divisions more than had been anticipated. The
doom of Rumania was sealed.

[Sidenote: Retreating armies must reach defenses.]

What happened in the Russian effort to support Rumania is exactly what
has occurred in nearly all the drives that I have been in during this
war. An army once started in retreat in the face of superior forces can
hold only when supported _en bloc_ or when it reaches a fortified line.
The Germans with all their cleverness and efficiency were not able to
stop the Russian offensive of 1916 until they had fallen back on the
fortified lines of the Stokhod in front of Kovel. In the Galician drive
against the Russians in 1915, the armies of the Tsar were not able to
hold until they reached the San River, on which they fought a series of
rear-guard actions.

[Sidenote: Russian corps on Sereth line.]

So it was in Rumania. The Russian corps arriving on the installment plan
were swept away by the momentum