China and Japan have been isolated from Europe and the Middle East for a very long period of time, and there's multiple reasons for that, with some fo the most important being:
- Geography;
Japan was an island, far away from Europe and the Middle East, and since they were not orientated towards sailing and exploration, not the civilizations of Europe and the Middle East went so far, they remained isolated. China is surrounded with natural barriers that made it hard for communication with this regions, there's deserts and the taiga on the north, deserts on the northwest, and the Himalayan Mountain range on the west and southwest.
- Self-sufficiency;
Both civilizations were in a way self-sufficient, sot hey didn't really had the need to explore and expand, especially not through regions that didn't seemed attractive.
- Safety issues;
The safety issues were a big problem. In order for the people of East Asia to come to the Middle East or Europe, they had to move through the Eurasian steppes, and in here were roaming the hostile nomadic tribes like the Mongols, Turks, and North Iranians, so any travel through this region was going to be doomed.