Emperor at home, king abroad

Emperor at home, king abroad was a system of conducting relations between states within the Chinese cultural sphere.

As China was a hegemonic power in East Asia for a large part of history, surrounding states were compelled to pay tribute to Chinese emperors in exchange for peace and political legitimacy.

When the Qin dynasty fell, general Zhao Tuo conquered the commanderies of Xiang and Guilin and proclaimed himself "Martial King of Nanyue" (南越武王; Nányuè Wǔ wáng) and in 196 BCE he was recognized "King of Nanyue" (南越王; Nányuè wáng) after Liu Bang became emperor and founded the Han dynasty.

After Liu Bang's death, his officials petitioned his widow Empress Lü to forbid trade in iron between Nanyue and Han; upon hearing the news, Zhao proclaimed himself "Martial Emperor of Nanyue" (南越武帝; Nányuè wǔ dì), on par with the Han emperors.

However, Zhou's troops fell ill because of the heat and dampness and thus failed to cross the mountains to enter Nanyue; later, they were recalled in 180 BCE after Empress Lü's death.

Frightened, Zhao wrote a letter of apology, humbled himself as a feudal subject of the Han Emperor, promised to offer tributes, and publicly announced in Nanyue that he would relinquish imperial title and practices.

However, Zhao still secretly designated himself as "Emperor" (帝; dì) inside Nanyue and only used titles appropriate for a tributary feudal lord like "king" (王; wáng) when sending envoys to the Son of Heaven.

[10] Following the First Sino-Japanese War, Joseon regained its independence from China and with the King Gojong becoming the Hwangje [ko] (황제) of the Korean Empire.

The system continued to be used until the end of the dynasty itself, as all rulers claimed imperial status domestically and reverted to royal rank when dealing with China.

Chinese emperors originally referred to Japanese rulers as the King of Wa (倭王), while they were called kimi or ōkimi in Japan.

During the Nanboku-chō period of Japan, Prince Kaneyoshi refused to accept the title of king granted by China, and killed seven Chinese ambassadors in retaliation.

The shogun Ashikaga Yoshimitsu accepted the title King of Japan bestowed by the Yongle Emperor due to his desire to establish trade relations with the Ming dynasty.