The Art of War by active 6th century B.C. Sunzi

6. Ground which forms the key to three contiguous states,

[Ts’au Kung defines this as: "Our country adjoining the enemy’s and a third country conterminous with both." Meng Shih instances the small principality of Cheng, which was bounded on the north-east by Ch’i, on the west by Chin, and on the south by Ch’u.] so that he who occupies it first has most of the Empire at his command, [The belligerent who holds this dominating position can constrain most of them to become his allies.] is ground of intersecting highways.