China and Japan are, of course, two different countries and some of their reasons for wanting to shut themselves off from European trade were different. Let us look at the reasons that were the same and the reasons that were different.
The one reason that is somewhat similar is that both countries believed that they were better than the Europeans. China, of course, had been a major civilization for a very long time when the Europeans arrived. Up until very recently, China had been the most advanced country in the world and the Chinese did not really understand that Europe had surpassed them in technology. China felt that it was the “Middle Kingdom,” superior to all merely human countries. Japan, too, felt that it was superior. Japanese were not impressed by the manners and the hygiene of the Europeans who made it to Japan. Japan felt that it was the country of the gods and was therefore superior to Europe as well.
China, but not Japan, felt that it had everything that it needed. China controlled a vast amount of territory with many resources. It did not feel that there was any reason to need to trade with the Europeans. Japan, but not China, was very concerned that Christianity could disrupt its society. Japanese who had become Christian were upsetting the very hierarchical nature of Japanese society. The Japanese did not want their culture and society changed by Christianity and other European ideas. This was a major reason for Japan’s decision to practically close itself to European trade.
These are some of the main reasons why these two countries attempted to cut themselves off from trade with Europe.