Having identified Vietnam as a key actor in solving the Cambodian problem and restoring peace in Southeast Asia, Japan carried out a policy of engagement with Hanoi. Tokyo’s objective was to induce the Vietnamese to soften their stance on the Cambodian problem and to loosen their ties with the Soviet Union which, taking advantage of the Cambodian situation and of the Sino–Vietnamese rivalry over it, had gained access to Vietnamese military bases. From those bases, it had become easier for the Soviets to conduct their military activities in the South China Sea, hence posing a threat to the sea lines of communication through which vital supplies of oil were shipped to Japan. This became an additional incentive for Japan to settle the Cambodian conflict and to try and make Vietnam “neutral” through a policy of positive engagement and of improvement of ASEAN–Vietnam relations. However, this Japanese line became increasingly at odds with the firm US stance toward Hanoi, which was aimed at isolating Vietnam and bleeding it dry.