In spite of the fighting, the leaders of reunified Vietnam and Kampuchea made several public diplomatic exchanges throughout 1976 to highlight the supposedly strong relations between them. However, behind the scenes, Kampuchean leaders continued to fear what they perceived as Vietnamese expansionism. Therefore, on 30 April 1977, they launched another major military attack on Vietnam. Shocked by the Kampuchean assault, Vietnam launched a retaliatory strike at the end of 1977 in an attempt to force the Kampuchean government to negotiate. The Vietnamese military withdrew in January 1978, even though its political objectives had not been achieved; the Khmer Rouge remained unwilling to negotiate seriously.