China, Russia and the Central Asian states of Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan formed the Shanghai Co-operation Organization (SCO) in 2001. China's backing for an SCO charter, permanent secretariat and anti-terrorism centre for the past three years reflects its desire to strengthen the SCO in countering United States influence in Central Asia. Diplomatically, China fears that the American presence means that regional states will be less accommodating to China's political demands. Economically, China worries that the United States' support for American petroleum companies will compromise Chinese efforts to wrest concessions from Central Asian governments. Security-wise, with bases close to China's western borders, Washington can assist Beijing in flushing out Xinjiang separatists operating in Central Asia, or put military pressure on China, should it be perceived as a threat. The American presence and resurgent Russian involvement in Central Asia seem to have put China's influence in the region on the defensive.