During a visit to Australian on Wednesday, President Obama announced that 2,500 U.S. troops will be sent to the country to boost security in the Pacific region. The move is seen as a strategy to counter China's increased influence. He  spoke strongly  on China's rising responsibilities and the U.S. perspective on its growing strength. China responded by saying that it "may not be quite appropriate" to expand U.S. military in the region. Dr. Zhiqun Zhu  is associate professor of political science and international relations at Bucknell University  and the MacArthur chair of East Asian politics. He talks about the changing relationship between the U.S. and China. Nick Bryant, BBC correspondent based in Sydney, reports on the latest from Obama's visit.