Chapter 6, Verses 14 and 15 - Sun Tzu

We can form a single united body, while the enemy must split up into fractions. Hence there will be a whole pitted against separate parts of a whole, which means that we shall be many to the enemy's few. And if we are able thus to attack an inferior force with a superior one, our opponents will be in dire straits.
~ from The Art of War, Giles translation ~

Go here to read the introductory post to the verses of The Art of War.