“With the United States in an isolated position, we would have to face the probability that the Soviet Union would quickly dominate most of Eurasia, probably without meeting armed resistance. It would thus acquire a potential far superior to our own, and would promptly proceed to develop this potential with the purpose of eliminating our power, which would, even in isolation, remain as a challenge to it and as an obstacle to the imposition of its kind of order in the world. There is no way to make ourselves inoffensive to the Kremlin except by complete submission to its will. Therefore isolation would in the end condemn us to capitulate or to fight alone and on the defensive, with drastically limited offensive and retaliatory capabilities in comparison with the Soviet Union” (NSC-68 1950).
NSC- 68: see the full report here.