What landform might have prevented the empire from expanding further east?

There are many landforms that can prevent expansion - bodies of water, mountainous terrian, and a desert are some examples.

The answer to this would depend on the empire we are referring to. However, there are several landforms that could potentially prevent any empire from expanding further east. For example, one of the most common barriers for empires were large mountain ranges. These were often too difficult to be crossed efficiently and regularly. Other landforms would include large deserts and oceans.