In a small sign of closer relations between the United States and Vietnam, Hanoi released two political prisoners on Monday before their sentences had been completed. Vi Duc Hoi and Nguyen Tien Trung, the Associated Press reports, were released yesterday; they join another prominent activist, Cu Huy Ha Vu, who was freed by the Vietnamese authorities earlier this month.Vietnam and the United States are in the middle of a free trade deal that is expected to boost Vietnam’s economy. Many political prisoners still languish in prison in Vietnam, though the release of a small handful is a sign that Hanoi wants to ingratiate itself with Washington. The main motivation for this effort is not hard to discern: China.Vietnam and China have had a fraught relationship for centuries. Vietnamese museums are full of artifacts glorifying resistance to the country’s overpowering northern neighbor. Though they share some of the same political and economic realities, China and Vietnam have found themselves on opposite sides of an increasingly ugly dispute over the South China Sea.Indeed, Vietnam recently put aside its differences with the Philippines over territorial ownership in the South China Sea and invited Filipino sailors to a party on an island that Vietnam had snatched in 1975. Vietnam has even hosted American ships at its ports, and the two countries have held joint naval exercises in the past few years. There are signs that Vietnam is also cozying up to Japan.A network of alliances and cooperative relationships is emerging in south and east Asia to combat China’s increasingly aggressive rise.