Tundra and cold temperatures kept the Chinese
from expanding in which direction?

Northern direction.

Explanation:

The Chinese have developed one of the earliest civilizations in the world and it has managed to persist for millenniums. Unlike many other civilizations though it is easily noticeable that the Chinese remained in roughly the same area for more than 2,000 years, which might seem weird considered the power of the country and that it was more than capable to expand throughout history.

There were several reasons as to why China did not expand further and one of them is the climate. China never expanded northwards an it didn't really seemed to be interested in it. Not just that they would have had to have open wars on open ground with the Mongol and Turkic tribes, but what they would have got int their territory would have been taiga and tundra. Both of these places are not of much use for a civilization, with the main problems being the extremely low temperatures and lack of resources.

sorry i really dont know