Letter, Central Committee of the Communist Party of the Soviet Union to the Chinese Communist Party, on the Soviet Union's Readiness to Provide Assistance to China in the Event of an Attack

... Comrade Gromyko informed us about his conversation with Comrade Zhou Enlai which took place in Peking on 7 September.  Comrade Zhou Enlai said that in the consideration of the situation in the Taiwan region the Politburo of the Central Committee of the Communist Party of China proceeded from the fact that should the USA start a war against the People’s Republic of China and in this event uses tactical nuclear weapons, then the Soviet Union will make a stern warning to the USA but will not take part in the war.  Only in the event that the United States uses large yield nuclear weapons, and in this way risks widening the war, will the Soviet Union make a retaliatory strike with nuclear weapons.

We carefully considered this issue and decided to express to you our opinion... We cannot allow the illusion to be created among our enemies that if an attack will be launched against the PRC by the USA or Japan—and these are the most likely adversaries,—or by any other state, that  the Soviet Union will stand on the sidelines as a passive observer.

Should the adversary even presume this, a very dangerous situation would be created. It would be a great calamity for the entire Socialist camp, for the Communist working class movement, if, when atomic bombs have begun to fall on the Chinese People’s Republic and China has begun to pay with the life of its sons and daughters, the Soviet Union, possessing terrible weapons which could not only stop but could also devastate our common enemy, would allow itself not to come to your assistance. This would be a  crime before the world working class, it would be a retreat from the holy of holies of the Communists—from the teaching of Marxism-Leninism.

Thank you for your nobility, that you are ready to absorb a strike, not involving the Soviet Union.  However, we believe, and are convinced, that you also agree that the main thing now consists of the fact that everyone has seen—both our friends and, especially, our enemies—that we are firm and united in our understanding of the tasks, which flow from Marxist-Leninist teaching, to defend the camp of Socialism, that the unity of all brother Communist parties is unshakeable, that we will visit a joint, decisive rebuff to the aggressor in the event of an attack on any Socialist state.  This is necessary so that no hopes will arise in our enemies that they will be able to separate us, so that no cracks will be created which the enemy could be able to use to break the connection between the Socialist countries.

...It is necessary that neither our friends nor our enemies have any doubts that an attack on the Chinese People’s Republic is a war with the entire Socialist camp.  For ourselves we can say that an attack on China is an attack on the Soviet Union.  We are also convinced that in the event of an attack on the Soviet Union the Chinese People’s Republic would fulfill its brotherly  revolutionary duty.  If we in this way will build our policy on the bases of Marxism-Leninism, depending on the unity of our goals, on the might of our states, on our joint efforts, the uniting of which is favored by the geographical disposition of our countries, then this will be an invincible shield against our enemies....