On 2 March 1969, Chinese and Soviet troops started fighting on Zhenbao Island (珍宝岛), a small island in the Ussuri river on the border between China and (at that time) the Soviet Union. This led to further escalation of the conflict between the two countries, and even to the threat of using nuclear weapons.
The main image on this poster is taken from Guan Qiming's 1969 painting "Increase vigilance, defend the motherland!".
The poster advertizes a documentary movie by the Central News and Documentary Studio (中央新闻纪录电影制片厂摄制).