In ancient times, China's geography included natural barriers of fierce deserts and the Himalayan Mountains.
The Himalayans are not located in modern day China. China's borders have changed over the years. Today, the Himalayans run along near the border of modern day southern China. Just as in ancient imes, the Himalayans are very high mountains. Ten of the highest mountain peaks in the world are found in the Himalayans, one of which is Mount Everest, the very highest peak in the world.
It has always been very difficult to climb over the Himalayan Mountains. In ancient times, since people could not climb over them, they had to find a way through them, and that was tough. So the Himalayans helped to protect the early people who settled in the interior of China from invasion.
For many thousands of years, China was isolated from the rest of world, in great part due to her natural barriers.