A recent article in the Dong-a Ilbo cites evidence obtained and disseminated by NKIDP to explain why North Korea did not criticize South Korea following the declaration of the Yushin Constitution in October 1972.
According to the article, despite the historic July 4, 1972, Joint Communiqué that marked a high point in inter-Korean relations, later that year in October, President Park Chung Hee of South Korea declared the Yushin Constitution. Both the friendly US and the hostile DPRK remained remarkably silent regarding this development.
According to documents released by the Woodrow Wilson Center’s North Korea International Documentation Project in cooperation with the University of North Korean Studies in Seoul, North Korea revised its initial plan to criticize the South Korean government because it wanted to maintain its leverage for the peaceful reunification of the Korean Peninsula through dialogue. It chose to continue its aggressive peace offensive strategy to eventually establish a unified communist Korea.
The United States, on the other hand, did not intervene for the sake of stability on the Korean peninsula. The US government did not want to undermine Park Chung Hee and make him susceptible to North Korean criticisms or attacks.
To view the article in Korean, please see the following link: http://news.donga.com/Politics/3/00/20121016/50132794/1.