Coalition of the Royal Family and the Nobility
In AD 3 16 the last emperor of the Western Jin Dynasty surrendered to other invading tribes. The following year, Sima Rui, a great-grandson of Sima Yi, restored the throne in Jianye (today's Nanjing). His dynasty was to be known as the Eastern Jin, and he became Emperor Yuan Di.
Sima Rui and his fugitive government were not highly thought of by the local nobilities of southern China. These were the interrelated big families that traced their ancestry to the Wu Kingdom in the Three Kingdoms period, and who had continued to prosper after the annexation of their state into the Western Jin. They were wealthy and looked down upon the northerners, calling them "rustics." Their contempt worried Wang Dao, a gentleman from the north, for despite Sima Rui's arrival a month before none of these noble families had cared to pay him homage. Wang Dao discussed the situation with his cousin Wang Dun, trying to devise a plan to win over these southern nobilities.
The third day of the third lunar month was celebrated across southern China as a day when people went to the riverside to pray for good fortune and to cleanse themselves of any ills, so Wang Dao decided to arrange a big outing for Sima Rui when everybody would be out and would see him. On this festive day in 307, Sima Rui made an appearance in his elaborate carriage, parading past the celebrating crowds, followed by Wang Dao and Wang Dun. The local people were very impressed, as were the noblemen. They changed their minds and extended the olive branch.
Next, Wang Dao reminded Sima Rui that he needed Gu Rong and He Dun, two of the most celebrated nobles, to join him in his government, so that the other big families would pay allegiance as well. On their part, the southern nobles were also starting to feel the need to enter into a coalition with the royal family from the north, with invading tribes from the north becoming a constant threat, while refugees pouring into the south were prone to riot. Seeing that a coalition would be in the interest of nobility from both the north and the south, Gu Rong and He Dun accepted the offer to join Sima Rui's government.
Because of the important role Wang Dao played in the founding of the Eastern Jin, many members of his extended family were given prominent positions in the government. So greatly did the royal family depend on the nobility, that people thought of the Wang family as sharing sovereignty with the Sima family.