Final answer:
Mountain ranges and deserts are natural barriers to expansion.
Step-by-step explanation:
Mountain ranges and deserts formed natural barriers to expansion.
Mountain ranges, such as the Himalayas, can act as a physical barrier between regions. For example, the Himalayan Mountains form a natural boundary separating India and China.
Deserts, like those found in Sub-Saharan Africa, can also act as natural barriers because they have limited resources and are difficult to traverse.