You have to understand Chinese geography and history about this.
First of all, why is China isolated?
The China Proper has the Pacific Ocean to the east and south. To the southwest, there is the Tibetan highlands. To the west and north, they were desert and frigid climate. It was very enclosing geography.
In the age before sophisticated ship-building technology, and long-term survival ability in the desert and frigid weathers, China Proper was isolated from the rest of the world, in the sense that there were seldom threats of wiping out the mainland culture. The northern tribes could not get past Chang Jiang (a.k.a. Yangtze River) and control the entire China Proper.
Until the Mongolians and the Yuan Dynasty suppressed the Chinese culture by conquering all of China Proper.
Coincidentally, China led the world in technology up until that point. China was self-sufficient. Heck, children these days are still taught to this day about how China is very large, therefore it can produce everything that everybody needs, and how it only choose to import from the outside world. (With the current trade war, we all know that’s not true anymore.)
Anyways, as you know, the Chinese people worship tradition, and the structure of the government is one of them. Although the structure gradually evolved in time, no dynasty really made any sudden big changes. It used to be like a big corporation, where the CEO delegates out different duties, and the department heads have authority to initiate orders without seeking approval from the CEO.
The Yuan Dynasty broke the traditional Chinese government structure. When Ming Dynasty came around, under the rule of Zhu Yuanzhang, who had no understanding on how to run a country (because he grew up as a thief and a monk), and even less trust in his followers, the government structure turned into an absolute monarchy, in which only the emperor has the authority to initiate any orders.
That is when China began to fall behind. Absolute monarchy comes with xenophobia, and are ultra-conservative, because they have no time to understand new ideas, which they don’t know if the new ideas can be used to overthrow their rule.
They closed themselves in and tried to keep everything status quo forever, or at least until they die.
In conclusion, isolationism is not in itself bad, given that you are self-sufficient. It is the attitude of the leaders that matters the most.
In the western world, no country has ever been self-sufficient. Most, if not all, countries rely on trading, such that isolationism has been given a negative connotation. When studying China, one needs to remove himself from the kind of “you must trade” idea.
It is because of isolationism that Ancient China required experts in literally everything in life, and that is the reason Ancient China could develop all kinds of new technologies in everything.
In the western world, each country is like a company that specializing in a few things, and they trade with each other. That is the opposite of China. China is a conglomerate that does everything.
Thanks,
Eddie