Bit of a long post.
The key is national identity. The concept of a nation state is a recent one and in pre-modern times loyalty/identity in the vast majority of the world's polities including East Asia was determined by deference to religion or your sovereign rather than "country." In my view though, China and by extension the Sinosphere already had some early concepts of statehood or at least underlying cultural factors that made its transition to modern nationhood smoother than in other parts of the world. It maintained cultural and linguistic continuity, superstition was rife and religions like Buddhism and Taoism existed but by and large the government maintained strict control over the proliferation of such beliefs, and it had an organized bureacracy through which to maintain the territories rather than relying on feudal lords.
You contrast this with the rest of the world. Let's not speak of the other Middle-Eastern nations like Syria and Libya, which are artificial colonial creations and thus the concept of nationhood just never took root, with everyone preferring to stick with their own tribe. But even for Iran, where they can claim some lineage dating back to the Persian Empires of past. Although Persian culture remained influential in the medieval world, what separates Iran from China, which had periods of barbarian rule, was that Chinese culture always remained front and center in these barbarian dynasties. Whereas for all the talks of how Persian culture endured in the Islamic world, it was never front and center, but one of the players in the orchestra sharing seats with the religion of Islam and the culture of the Turkic tribes that founded the empires. So while Persian is for sure a long lasting and great culture, it was never able to maintain civilizational autonomy the same way Chinese did. Let's not forget too while China is 90% Han, Iran is only 60% Persian, so there plenty of other people there who have their own views of sovereignty and varying degrees of identifying with "Iranism."
I can go on longer, but Sinitic civilization made it so that even in the 1900s when Korea, China, and Vietnam were under everyone's boot heel it wasn't hard to promulgate a sense of unified identity that even illiterate peasants were willing to die for. The Middle East including Persia was always just way too fractured to convince the peoples there to buy into the concept of nationhood, let alone get them to die for it.
