US Defense Secretary Robert Gates is scheduled to visit China starting on Sunday at the invitation of State Councilor and Defense Minister Liang Guanglie.

The visit symbolizes the normalization of the interrupted high-level military exchanges, and will help promote good interaction and broader relations between China and the United States. It will also pave the way for President Hu Jintao's visit to the US due to start on Jan 19.

Military ties have always been the most sensitive weathervane of relations between the two countries and Sino-US military ties have gone beyond the military scope and been endowed with a highly political responsibility.

In the past decades since normalization of diplomatic ties between China and the US, military needs, for a long time, played an important role in driving the development of bilateral ties, in addition to their unified front against the perceived military threat from the then Soviet Union. However, the disappearance of the Soviet threat quickly put military ties between Beijing and Washington in a particularly vulnerable position and ever since bilateral military ties have been affected from time to time by their political relations.

Currently, Sino-US relations remain generally stable and bilateral cooperation remains smooth on a range of important global and regional issues, as common interests override disagreements on some issues. However, security and military exchanges have long lagged behind exchanges in other fields.

Lack of mutual trust has proven to be the biggest obstacle to good Sino-US military ties. Despite their efforts to avoid direct conflicts, the military forces of both countries seem to look upon the other as the largest potential threat. The risk of military conflicts between China and the US over the Taiwan question has subsided in recent years, but the root cause for such Sino-US clashes has not been completely eradicated.

The Anti-Secession Law commits the Chinese government to take all available measures, including military ones, to oppose and check Taiwan's split from China.

At the same time, the US' Taiwan Relations Act allows the US to provide "defense services in such quantity" it deems necessary to Taiwan. Such legislation makes a head-on military confrontation between China and the US over the Taiwan question a real possibility.