The closing of an avenue of approach, the security of a single road or river, or even the strategic movement of a small body of troops, often effects, in the beginning, what afterwards cannot be accomplished by large fortifications, and the most formidable armies.

Had a small army in 1812, with a well-fortified depot on Lake Champlain, penetrated into Canada, and cut off all reinforcements and supplies by way of Quebec, that country would inevitably have fallen into our possession.

In the winter of 1806-7, Napoleon crossed the Vistula, and advanced even to the walls of Koenigsberg, with the Austrians in his rear, and the whole power of Russia before him.

If Austria had pushed forward one hundred thousand men from Bohemia, on the Oder, she would, in all probability, says the best of military judges, Jomini, have struck a fatal blow to the operations of Napoleon, and his army must have been exceedingly fortunate even to regain the Rhine.

But Austria preferred remaining neutral till she could increase her army to four hundred thousand men.
She then took the offensive, and was beaten; whereas, with one hundred thousand men brought into action at the favorable moment, she might, most probably, have decided the fate of Europe.
"Defensive war," says Napoleon, "does not preclude attack, any more than offensive war is exclusive of defence," for frequently the best way to counteract the enemy's operations, and prevent his conquests, is, at the very outset of the war, to invade and cripple him.