When the Europeans decided to spread their imperialistic forms further, their style was changed in a sense that they weren"t dealing with an "uncivilized" country as they had with Africa and such other countries. European countries did not build schools or hospitals in China nor did they set up European-run governments in China. European countries never had "any real" colonies in China. China's central government was particularly strong for much of the time that the Europeans were there. Conclusions come that imperialism by the Europeans in China did not take place by colonization but through a sphere of influence. Basically a sphere of influence is an area where a foreign country has the right to trade. Usually other countries do not have the right to trade in that country's sphere of influence and also a country with a sphere of influence can have say in the policy of the country it is in.
Europeans were afraid that if there was no real government in control, they could not trade the way they want, so they helped keep the ruling dynasty in power at that time. They even went to limits to send armies to help the Chinese government keep their power over its people in control. The European intentions in China were to just try to gain as much as they could for themselves.
China had many things that the Europeans wanted to buy from them. Some things included china, silk as well as tea. Europeans had their eyes on other raw materials that China produced as well. But the "want" was not vice versa. The Chinese were very ethnocentric and felt that most of what they had was much better than that what other countries had. In the Chinese eyes, Europeans were barbarians and by the 1800's the Europeans had begun to think that the Chinese were the barbarians.
Opium was one thing that the Europeans, British in particular, had found something that the Chinese had wanted. Opium was a drug that people had become addicted to and spent a lot of money on.