China may be said to confront four current categories of challenge. The first is easiest and comes from the island entities and states in southern Chinese waters who challenge China's claim to complete sovereignty in the region, comparing its rivals there with the minor states and monarchies that in the past recognized the supremacy of the Middle Kingdom and paid tribute to it.
In the long term, China's leaders assume that such a relationship with its China Sea neighbors will eventually be restored, and this seems not unlikely. Vietnam, which seceded from China in the tenth century, would seem the most likely to maintain its independence.
The second threat is a great rival state of its own rank capable of challenging its government and imposing its own sovereignty or dynasty.