From the Copenhagen climate change conference to Internet freedom to China's border with India, China observers have noticed a tough tone emanating from its government, its representatives and influential analysts from its state-funded think tanks.

Calling in U.S. Ambassador Jon Huntsman on Saturday, Chinese Vice Foreign Minister He Yafei said the United States would be responsible for "serious repercussions" if it did not reverse the decision to sell Taiwan $6.4 billion worth of helicopters, Patriot Advanced Capability-3 missiles, minesweepers and communications gear. The reaction came even though China has known for months about the planned deal, U.S. officials said.

"There has been a change in China's attitude," said Kenneth G. Lieberthal, a former senior National Security Council official who is currently at the Brookings Institution. "The Chinese find with startling speed that people have come to view them as a major global player. And that has fed a sense of confidence."

Lieberthal said another factor in China's new tone is a sense that after two centuries of exploitation by the West, China is resuming its role as one of the great nations of the world.

This new posture has befuddled Western officials and analysts: Is it just China's tone that is changing or are its policies changing as well?