Vietnam's balancing of power act, namely the policy of seeking a counterweight to the China threat, and the politics of the U.S.-Vietnam-China triangle, may have taken shape in the early years of the twenty- ?first century, but it was deeply rooted in the changing relations between the big powers in the 1980s and Vietnam's need to adjust its policy to these changes. A combination of factors - geographical proximity, ideological affinity, and the need for regime survival - tends to make Vietnamese leaders more comfortable with China than with the United States. Only the perception of China as a bullying neighbour would push Vietnam to opt for a different orientation and adopt an antagonistic policy towards China. Meanwhile, United States-Vietnam relations in turn are affected by two factors: Vietnam's sensitivity to China's concerns and its mistrust of U.S. intentions. Bilateral relations became warmer mainly after Vietnam took steps to overcome its mistrust of the United States. China's recent assertive behaviour in the South China Sea worries Vietnam and threatens the U.S. position in the Asia- ?Pacific, and this has led to a convergence of strategic interests between the United States and Vietnam.