ter of fact, it would have been extremely
difficult to take Warsaw by a frontal attack. Warsaw's weakness
lay in the north in the swamp regions.

One of the greatest dangers in all wars, against which a military
commander has to guard his army, is that of being flanked. The road
or roads leading from the rear to the base of supplies, along which
not only food supplies for the soldiers, but, quite as important,
ammunition, is brought up, either in wagons, automobiles, or in
railroad trains, are the most sensitive part of an army's situation.
Unless they are very short--that is, unless an army is very close
to its base of supplies--it is impossible to guard these lines
of communication adequately. Therefore, if the enemy is able to
break through on either side of the front, there is great danger
that he may swing his forces around and cut these lines of
communication. The army that is thus deprived of its sources of
supply has nothing left then but to surrender, sometimes even to
inferior forces. Sometimes, of course, if the army is within the walls
of a fortified city and is well supplied with food and ammunition,
it may hold out and allow itself to be besieged. This may even
be worth while, for the sake of diminishing the enemy's strength
to the extent of the forces required for besieging, usually many
times larger than the besieged force. But in the case of Warsaw
we shall see that that would not have been a wise plan; hardly
any food supply that could have been laid by would have maintained
the large civil population, and the big guns of the Germans would
soon have battered down the city's defenses.

This the Russians realized from the very beginning. As is well
known now, Russia had never intended to hold Poland against the
Teutons. Her real line of defense was laid much farther back. It was
only on account of the protest of France, when the two Governments
entered into their alliance, that any fortifications at all were
thrown up in Poland. A real line of defense must be more or less
a straight line, with no break. And the marshes in the north, as
well as the tongue of East Prussia projecting in along the shores
of the Baltic toward Riga made that impossible. Russia's real line
of defense was farther east, along the borders of Russia proper
and along the line of railroad already referred to. By studying
this territory east of Poland it will become obvious why Russia
should prefer this as her main line of defense