June 1982, at an event in Kuala Lumpur, the Khmer Rouge were among the factions declaring the formation of a Coalition Government of Democratic Kampuchea (CGDK) as an alternative to the administration in Phnom Penh. On the ground in Cambodia there nevertheless remained little military collaboration between these factions, which included the Khmer Rouge as well as the Sihanoukist National Army and Son Senn's National Front for the Liberation of the Khmer People. In 1983, Pol Pot travelled to Bangkok for a medical check-up; there he was diagnosed with Hodgkin's disease. In mid-1984, Office 131 was moved to a new base further into Cambodia, near the O'Suosadey river. In December, the Vietnamese Army launched a major offensive, overrunning the Khmer Rouge's Cambodian base and pushing Pol Pot back into Thailand. There, he established a new base, K-18, several miles outside Trat. In September 1985, Pol Pot resigned as commander-in-chief of the Khmer Rouge forces in favour of Son Sen; he nevertheless continued to wield significant influence. In the summer he married a young woman named Mea; the following spring their daughter, Sitha, was born. He then travelled to Beijing to undergo cancer treatment at a military hospital, only returning to Cambodia in the summer of 1988. In 1988, the anti-Vietnamese factions entered into negotiations with the Phnom Penh government. Pol Pot deemed this too soon, for he feared that the Khmer Rouge had not gained sufficient popular support to produce significant gains in any post-war election. Fall of the Khmer Rouge: 1990–1998 The fall of the Berlin Wall and the subsequent end of the Cold War had repercussions for Cambodia. With the Soviet Union no longer a threat, the U.S. and its allies no longer saw Vietnamese domination of Cambodia as an issue. The U.S. announced that it no longer recognised the CGDK as the legitimate government of Cambodia at the UN General Assembly. In June, the various Cambodian factions agreed a ceasefire, to be overseen by the United Nations, with the formation of a new Supreme National Council to facilitate the implementation of democratic elections. Pol Pot agreed to these terms, fearing that if he refused the other factions would all unite against the Khmer Rouge. In November, Sihanouk returned to Cambodia. There, he praised the Vietnamese-backed leader, Hun Sen, and stated that the Khmer Rouge's leaders should be put on trial for their crimes. When Samphan arrived in