As previous commentators have noted, China is now inextricably bound to many other countries, perhaps the most important of which is the United States. China is one of our primary creditors, and as such, its financial well being is now dependent upon the financial health of the United States. In addition, as a country whose industries are among the fastest growing in the world, China requires increasing volumes of imported petroleum to fuel its industrial growth, which means that its future is now also tied to the Middle East's ability to remain stable enough to export petroleum continously.
China's traditional cultural and political insularity is undergoing a sea change as its economy develops and becomes dependent on the economies of countries with which it used to have very little in common. And as China continues to develop a middle class--an unavoidable consequence of dramatic economic development--this new middle class will itself develop power that China's government may not be prepared to accommodate.
Clearly, the outside world now dramatically influences China's development, but the question remains, "Will China embrace the changes working their way through its culture and politics."
There is almost no country today that is not influenced by the outside world. China is definitely affected by other countries, including America. China has been adapting its economy to a more capitalistic form.
It has a centrally planned economy which is in the process of dismantling the institutions of state ownership and control it borrowed from its former ally, the Soviet Union. (see first link)
Many American companies have opened up shop in China, but not all have succeeded. For example, while Wal-mart has done well in China, Home Depot recently had to re-evaluate its progress.
"China is a do-it-for-me market, not a do-it-yourself market, so we have to adjust," Home Depot spokeswoman Paula Drake told Reuters late on Thursday. (see second link)
Apparently, Home Depot did not do enough market research. Chinese consumers prefer to have people do things for them, whereas Americans perfer to do things ourselves. Clearly not every American idea transfers cultures.
I don't believe that China is self-contained, and in my opinion it is proved by their huge stake of the U.S. national debt. China owns over a trillion dollars in American debt, and is continually adding on to that because it has a symbiotic relationship with the American consumer. Despite our political and philosophical differences China needs to employ its billion citizens with its export economy and American consumers "need" cheap manufactured goods from China. Until the world market expands to the point that the American consumer is no longer vital to the Chinese economy, it will not be self-sufficient.
The definitive answer to this question will be answered if China ever crashes the dollar by trying to cash in its debt. The day you see China try to replace the dollar with its own currency on a global scale and tries to call in its debt, that is the day you will know that China believes it no longer needs the United States.
Assuming that you mean the "was" of ancient Chinese history and that you mean "self-contained" and "isolated" as synonymous terms, we can look at the periods of Chinese history that produced some of the great inventions of China such as, for example, paper.
Paper's invention, though traditionally attributed to Ts'ai Lun in 105 AD, according to late archaeological evidence was earlier with signs of paper in 900 BC. Paper spread from China to Korea then to Japan, then to Vietnam and India (in that order) beginning in the 300s and ending in the 600s. The telling part about whether China was self-contained and isolationist comes when we think that, though paper came to spread around Asia for three centuries, it did not reach Europe until around 1100 and England until around 1490. This speaks of China's isolation and self-sufficiency (while also showing the isolation of the entire Asian.
I would argue that it is impossible, in the modern era, for a country as large and populous as China to be isolated. China has the world's second largest economy, which is only made possible by the fact that it has a vibrant and growing export economy.
That being said, China is also unique in world cultures and governments for its ability to follow its own path, and limit outside influence, at least in terms of policy. They tend to look at the long term, focus on their own interests, and patiently wait for other countries to adopt pragmatic policies towards them.
Access to the internet and international travel undoubtedly has an influence over time on China's population and government, even though the government still has absolute authority over the population and censors net access.
Is this meant as an "is" or a "was?" If we are talking about the present day, China is clearly influenced from the outside. The very fact that China was communist shows outside influence as communism is of European origin. The fact that it has moved away from economic communism shows it has been influenced by the outside world.
If we are looking at the past, it would help to know what era we are talking about. China was been influenced by the outside at least since the Opium Wars in the mid-1800s. Before that, it was much more insular, affecting the outside world more than it was affected by that world.