How was China protected?

China was protected historically by three natural barriers.

1. Gobi Desert: To the northwest of China is the vast and dry Gobi Desert, it became impassable for armies on horseback or for camel caravans for a good part of the year

2. Taklamakan Desert: China is further separated from India by Taklamakan desert, it presents almost the same obstacles as Gobi

3. Himalayas: India shares the long range of Himalayas with Tibet , an autonomous region of China which acts a formidable barriers between the two great civilizations of eastern Asia