Simply put, China has three core strategic interests.
Paramount among them is the maintenance of domestic security. Historically, when China involves itself in global trade, as it did in the 19th and early 20th century, the coastal region prospers, while the interior of China -- which begins about 100 miles from the coast and runs about 1,000 miles to the west -- languishes. Roughly 80 percent of all Chinese citizens currently have household incomes lower than the average household income Bolivia. Most of China's poor are located west of the richer coastal region; this disparity of wealth time and again has exposed tensions between the interests of the coast and those of the interior. After a failed rising in Shanghai in 1927, Mao Zedong exploited these tensions by undertaking the Long March into the interior, raising a peasant army and ultimately conquering the coastal region. He shut China off from the international trading system, leaving China more united and equal, but extremely poor.
The current government has sought a more wealth-friendly means of achieving stability: buying popular loyalty with mass employment. Plans for industrial expansion are implemented with little thought to markets or margins; instead, maximum employment is the driving goal. Private savings are harnessed to finance the industrial effort, leaving little domestic capital to purchase the output. China must export accordingly.
China's second strategic concern derives from the first. China's industrial base by design produces more than its domestic economy can consume, so China must export goods to the rest of the world while importing raw materials. The Chinese therefore must do everything possible to ensure international demand for their exports. This includes a range of activities, from investing money in the economies of consumer countries to establishing unfettered access to global sea-lanes.
The third strategic interest is in maintaining control over buffer states. The population of the historic Han Chinese heartland is clustered in the eastern third the country, where ample precipitation distinguishes it from the much more dry and arid central and western thirds. China's physical security therefore depends on controlling the four non-Han Chinese buffer states that surround it: Manchuria, Inner Mongolia, Xinjiang and Tibet. Securing these regions means China can insulate itself from Russia to the north, any attack from the western steppes, and any attack from India or Southeast Asia.