“It entered into a Treaty of Friendship, Cooperation, and Mutual Assistance with North Korea in 1961, containing a clause on mutual defense against outside attack that is still in force at this writing. But that was more in the nature of the tributary relationship familiar from Chinese history: Beijing offered protection; North Korean reciprocity was irrelevant to the relationship. The Soviet alliance frayed from the very outset largely because Mao would not accept even the hint of subordination.”
Book:On China