I would hardly argue that China has been prone to subjugation by nomad peoples. The Song Dynasty of China was conquered by the Mongols in the 13th century AD, but it is important to note that by this stage the Mongols were not nomads. They had been ruling over settled states for half a century, and used huge numbers of Chinese infantry and siege engineers.

Source: The Age of Confucian Rule: The Song Transformation of China, by Dieter Kuhn.

In actually, various Chinese dynasties thoroughly spanked nomadic armies. Examples include the campaigns of the Han Chinese against the Xiongnu in the 2nd Century BC, the Tang Empire against the Turks in the 7th Century AD and the Ming Dynasty against the Mongols in the 14th and 15th century AD. It is worth noting that conquest by nomadic powers usually occurred when a settled state was in a period of economic or political chaos/weakness. Whilst nomadic nations could have a higher proportion of their male population as warriors, their major weakness was attrition. It took a generation to raise someone to be a good horsemen and archer, whilst settled states could train and deploy troops much more quickly.

Sources:

China's Cosmopolitan Empire: The Tang Dynasty (History of Imperial China), by Mark Lewis.

The Early Chinese Empires: Qin and Han (History of Imperial China), by Mark Lewis.

The Troubled Empire: China in the Yuan and Ming Dynasties (History of Imperial China), by Timothy Brook.