The reason is actually simple, the two Jin And two Song Dynasties have places to be partial, but the Two Han Dynasty did not have.
The Eastern Jin Dynasty, the Southern Song Dynasty, and the Eastern Han Dynasty, were all reborn after the collapse of the dynasty, and were also called "Zhongxing" in history.
The temple name of Liu Xiu in the Eastern Han Dynasty was "Shizu";
Sima Rui of the Eastern Jin Dynasty had the temple name "Zhongzong";
The temple name of the Southern Song Dynasty Zhao Was "Gaozong".
That is to say, only Liu Xiu of the Eastern Han Dynasty called himself Zu, while Sima Rui and Zhao Zhuo were both emperors. The reason for this can be considered from two aspects:
1, the Eastern Jin Dynasty and the Southern Song Dynasty can only restore half of the country, the direct cause is naturally the lack of ability of Sima Rui and Zhao Zhuo.
Sima Rui himself was only a banner of the Gate Valve family, the king and Ma shared the world, Sima Rui became emperor by relying on the Langya Wang clan, and the Langya Wang clan relied on the Sima family to suppress the Jiangzuo family, and the two joined forces to gain a foothold in Jiangdong.
Zhao Shuo, nicknamed "Complete Yan Construct" by the present people, although there were "four generals of Zhongxing" to help him calm the southern rebel army and the separatist forces, he did not dare to duel with the Jin people and revive the Central Plains.
Neither of them could speak with Liu Xiu on the same day.
2, from the perspective of objective conditions, Liu Xiu has no conditions for partial security, and can only choose to chase deer in the Central Plains and win the world.
The development of the southern region by the mainland is another gradual process. For the area south of the Yangtze River, Sima Qian wrote in the "Chronicle of The Chronicle of Cargo Colonization":
"The land of Chuyue, the land is vast and sparsely populated, rice and soup fish, or fire cultivation and water, fruit clams, do not wait for Jia and enough, the terrain is fertile, there is no plague of hunger, there is no stolen life, there is no accumulation and there is much poverty, it is south of the old Jianghuai, there is no cold and hungry person, and there is no house of thousands of gold."
Therefore, the struggle for world domination at the time of the two Han Dynasties still has little to do with the south, and the areas where green forests, red eyebrows, and copper horses are active are also in the north.
Liu Xiu fought for the world, with Hebei as its foundation, and its unified world was comparable to that of the Warring States Seven Heroes of that year, and similar to that of the founding period of the Western Han Dynasty. At that time, the south did not yet have the conditions for partial security, so Liu Xiu would not objectively be partial to security.
The first time there was a divided force in the south began with the Three Kingdoms at the end of the Han Dynasty (eastern) and began at the Battle of Chibi, and Cao Cao faced the problem of north and south for the first time in the history of the mainland.
By the standards of Liu Bang and Liu Xiu, Cao Cao basically unified the "world".
The difference is that after four hundred years of development in the two Han Dynasties, during the Three Kingdoms period at the end of the Han Dynasty, Jiangdong and Bashu in the south joined forces and could already compete with the Central Plains.
Therefore, the Eastern Jin Dynasty was the first time that the Central Plains Dynasty crossed south, and it was also the first time that there were conditions for peace.
And the Southern Song Dynasty, is the second time.
As a result, those who have the conditions to be safe have become "drunk by the warm wind and directly make Hangzhou a state of Bizhou".
In contrast, in the Eastern Han Dynasty, at that time, there was no such condition, either to live or die, and there was no way to live.