Why did east asia turn into a long period of isolation?

为什么历史上东亚转入了长期孤立的状态?

I heard east Asia was in a period of isolation prior to European empires forcing them out of it. Why did they isolate themselves in the first place? Weren't China or Japan benefitting from trade with India or Indonesia or the silk road even? Or did they have enough resources to rely on themselves alone? How about the Siberian tribes or Mongolia, were they part of the isolation?

我听说东亚在欧洲帝国主义强行让他们开放之前都处于孤立之中。首先他们为什么要孤立自己?中国或日本甚至不是从与印度,印度尼西亚或丝绸之路的贸易中受益吗?还是他们有足够的资源来自给自足?西伯利亚部落或蒙古部落呢,他们也是孤立的一部分吗?