Wang (王) or Kings of the Han Dynasty can be divided into two categories: Yixing Wang （異姓王） or Kings and Tongxing Wang (同姓王) or Princes. Yixing Wang literally means "Wangs with a different family name than the emperors" while Tongxing Wang means "Wangs with the same family name as the emperors". Tongxing Wang were normally relatives of the emperors by direct male line.
It is arguable how to translate the Chinese "Wang" into English. In this article, "kings" is used for Yixing Wang because these Yixing Wang were generally derived from peer kings of Liu Bang, Emperor of Han. During the 2nd century BC, they had enormous power in their territories and were de facto sovereigns to some extent. After the 2nd century BC, these territories lost most of their regional autonomy, the kings lost executive powers, and their kingdoms' administrations were staffed and monitored by the central government. The kings did retain some rights, however, such as revenue sharing of the taxes collected by the central government in their nominal fiefdoms.
Tongxing Wang is translated as "princes" since they were normally sons or brothers of the emperors, and after the Rebellion of the Seven Princes, had relatively little power in their territories. In the early period of Han Dynasty there was no legal distinction between Yixing Wang and Tongxing Wang. The early princes were as powerful as kings in their territories.
Wang (Kings) were remnants of the rebellion against the Qin Dynasty. When the Qin Dynasty collapsed, many former nobles of the old Warring States joined the rebellion and occupied territories. They called themselves "kings" and often used the names of the old Warring States kingdoms to bid for support from the peoples of those states. Among these kingdoms, Chu was the most powerful. After the Qin Dynasty was overthrown, Xiang Yu, King of Chu, decided to align all the kingdoms for his own political advantage. After the alignment, 18 Kingdoms were formed. However, many of these kings were not satisfied with this arrangement and rebelled against Xiang Yu, among them Liu Bang, King of Han. Liu Bang later defeated Xiang Yu and became the first emperor of the Han Dynasty. The kings who had sided with Liu Bang in the Chu-Han Contention remained as kings under the Han Emperors; other kingdoms were created for generals and favorites of Liu Bang.
Although nominally under the rule of the Han Dynasty, these kings were de facto sovereigns, with very considerable power in their territories. Liu Bang felt this was dangerous to the unity of his empire, and endeavoured to subdue these unruly kingdoms. By conspiracies, wars and other political manoeuvres, many kings were deposed and their kingdoms annexed during Liu Bang's lifetime. When Liu Bang was dying, he ordered his ministers to swear an oath that only members of royal house of "Liu" could be created as Wang (i.e., Tongxing Wang or princes) under the Han Dynasty. In spite of this, some new Yixing Wang were created later, especially during the reign of Empress Dowager Lü. Most of these newly-created kingdoms were abolished after her death. The last king during the Han Dynasty was Wu Chan, King Jing of Changsha, who died without an heir in 157 BC. After that there were no further Yixing Wang for the remainder of the Han Dynasty until Cao Cao became the King of Wei in the last years of the Han Dynasty.
After establishing the Han Dynasty, Liu Bang created several Tongxing Wang, or principalities, for his relatives and sons. It then became a tradition that sons of Chinese emperors should automatically be created as princes. This tradition continued until the Qing Dynasty, in which sons of emperors could be created as lower nobles. Liu Bang and his successers originally thought that creating principalities for members of the royal family would strengthen the royal house and strengthen their hand against the kings (Yixing Wang). However, some of these princes became as powerful as those kings, and equally as dangerous to the emperor - or even more dangerous, because as members of the royal house, they were eligible to succeed to the throne, and were therefore potential pretenders.
Several rebellions or attempted rebellions by these powerful princes happened during the reigns of Emperor Jing and Emperor Wu, the most famous being the Rebellion of the Seven States. Subsequently, Emperor Wu removed most of the power of these princes and divided their territories, so that they would no longer be a threat to the throne. The institution of principalities would last throughout both phases of the Han Dynasty, however.
In the early part of the Han Dynasty, kings or princes were the rulers of their territories, usually including several prefectures. After Emperor Wu of Han, kings and princes were limited to acting as figurehead of their territories, whilst the real power was given to the prime ministers of these princes, who were appointed by the imperial court. Moreover, the princes' territories were reduced to only one prefecture.
The Crown Prince in the Han Dynasty was the heir apparent to the throne. The Crown Prince was normally the eldest son of the Emperor and the Empress, but not always. The power to nominate the Crown Prince lay with the throne, although the Emperor generally had to obtain the advice or consent of his high ministers. The Crown Prince would not be given a princedom, but rather abode with the Emperor in the capital. When a prince became Crown Prince, his princedom became extinct. The Crown Prince could be dismissed and this did indeed happen several times in the Han Dynasty.