evidence: The deal flowed from an initial agreement signed in 2004 by former Russian President Vladimir Putin that proposed a 50-50 division of the disputed islands. While Russia returns Yinlong and half of Heixiazi, totalling 174 square kilometres, China has given up its claim to the other half of Heixiazi. [...] The Heixiazi/Yinlong islands were seized by the Soviet army in 1929 during a skirmish with the Manchurian warlord, Zhang Xueliang. Through US arbitration, Zhang restored the Chinese Eastern Railway (a former Russian concession) to Soviet control in exchange for the withdrawal of Soviet troops from Manchuria. However, the Soviet army held onto the islands due to their strategic value. [...] Negotiations between the two countries over the status of Heixiazi took place in 1964. Beijing demanded acknowledgement of the "unjust" character of all the seizures of territories by Russia since the nineteenth century. Moscow refused to discuss the issue. The second round of talks in 1969 ended abruptly with the eruption of armed clashes over Zhengbao (Damansky) Island in the Ussuri River. Both sides massed millions of troops along their borders as tensions escalated.