Who brainwashed nationalism?
Nationalism is western culture. China didn’t have nationalism for two thousand years. Since Qin Shi Huang united China, China has had only the concept of Under the Haven (天下）， there has been no concept of a nation.
Nationalism comes with Opium War. Chinese diplomats cannot talk to Western powers as every one of them put national interest above justice and fairness. If you have power, you grasp all the interest you can, regardless it is right or wrong. That was the Opium War taught the Chinese what is nationalism. So they organized the Nationalist Party, or KMT according to sound translation.
After 1949, under Mao, China has no nationalism. China has only Internationalism. It was the Internationalism of Communist International. Supporting the world communist movement is the principle of Chinese foreign policy. Nationalism has no place in Chinese foreign affairs.
Nationalism comes into China again during Deng. China has to negotiate on WTO and many other International affairs and has to learn the language of international politics, the language of National Interest.
If Chinese nationalism is a result of brainwashing, it is the west brainwashing the Chinese. It is the west that put its political culture onto Chinese brains.
What is realpolitik? Who is playing realpolitik in International politics? Is there national interest without nationalism?
When the USA has its national interest in the South China Sea, the Korean peninsula, in Afghanistan, and put a military base in the areas surrounding China, who has expanded national interest more? Who has the stronger nationalism? And yet US people do not even notice how strong is their nationalism. That’s typical of brainwashing.