The international order of East Asia shifted considerably after the foundation of the Ming dynasty in 1368. In the era of Hongmu(1368-1398), Ming was facing two international agendas. One was to revise the China-nearby relationship that had originally been established by the Mongol Yuan empire. The other was to establish new relationships with regions that had not been officially affiliated with China since the 14th century. Regions in the former category included the Mongols in the north, the Jurchens in the Northeast, polities in Central Asia s northwest, and Tibet. All these regions were connected to China by land. Regions in the latter category included regions south and east, the Southeast Asian states, Ryukyu and Japan. These regions were connected to China by sea. The Ming government sent envoys to establish diplomatic relationship with all of these regions.
There were some characteristics shared by all the envoys that were dispatched to these regions. For envoys that would be dispatched to regions of the former category, which had prior relationships with Yuan, people who originally came from those regions, as well as merchants and Buddhist priests who had connections with those regions, were mobilized. For envoys for regions in the latter category, with which new relationships were to be attempted, eunuchs were drafted in most cases. Also, in case of the former, the Ming government wanted to utilize existing human resources and their institutional experiences inherited from Yuan, but in case of the latter, the Ming emperor wanted to use his own eunuchs. The Ming government wanted to insert all the inland regions of the former category into its military organizations(wei-so system), while other regions across the sea into the vassal states(tributary system).
The envoys sent to Goryeo during the Hongmu era included many eunuchs who were originally from Goryeo and had been serving in the Yuan court ever since. We can see that Goryeo was a case that involved both categories. Goryeo was very much close to the Yuan court, and was also re-designated as a tributary state under Ming s authority. In other words, Goryeo was the only country that inherited a legacy in terms of its relationship with Yuan, and was also integrated into the new Ming-centric international order of East Asia.
In the Yeong rak era, many of the envoys dispatched to foreign countries were eunuchs who had come to China from those very countries. We can see that the Hongmu era practice became a diplomatic convention for the Ming government in subsequent periods.