It took only seven years for Liu Bang to start his army in 209 BC and officially proclaimed himself emperor in 202 BC.
Where is Cao Cao?
In 189, Cao Cao stayed in Chen. Until his death in 220 AD, Cao Cao only laid half of the north.
As far as ability is concerned, Cao Cao is no worse than the founding kings of past dynasties. It's unfortunate that Cao Cao didn't unify the world all his life. Although Cao Cao's model may be different from that of Liu Bang, Li Shimin and Zhu Yuanzhang, this is not the fundamental reason why Cao Can cannot be unified.
Cao Cao is unlucky. What is the difference?
The strategic environment is grim.
Liu Bang and Li Yuan, they established the most powerful Han and Tang Dynasties in China, but their characteristics are the same? They are all fruit pickers.
What do you mean by picking fruit? That is, the people in front have already played almost, and only a few people are left in the final. Two men rushed up to kill these finalists and eat chicken directly.
When Liu Bang rose, the Chen Guang uprising shook the foundation of the Qin Dynasty. During the uprising, Liu Bang was never the key target of the Qin Dynasty. Qin Jun was too busy fighting the old nobles of the six countries to care about Liu Bang with mud legs.
Qin Jun finally appeared a Zhang Han who could fight and be fierce, and was killed by Xiang Yu, who was more fierce than him. At this juncture of the fierce battle between Xiang Yu and Qin Jun, Liu Bang secretly bypassed the main battlefield, occupied Xianyang and destroyed Qin in one fell swoop.
Even Xiang Yu didn't care about Liu Bang after the enfeoffment system, and Shandong governors opposed Xiang Yu everywhere. Before Liu Bang went through the customs, Xiang Yu had already become one with the Shandong governors, otherwise Liu Bang would not be given a chance to backstab and Cheng Peng (Liu Bang didn't win).
Tang Gaozu's situation is similar to that of Liu Bang. With the death of Emperor Yang Di, rebels spread all over the country, including before Yang Xuangan and after Wagang Army. The government forces of the Sui Dynasty have been exhausted by the rebels.
When the whole country was in a mess, Tang Gaozu shot the sniper quickly and occupied Chang 'an quickly, which was strongly supported by Guanlong Group. After occupying a solid foundation in Guanzhong, the Tang Dynasty waited patiently for the Kanto governors to kill each other. After the battle, Tang Jun marched eastward and killed Wang and Dou Jiande, and the world was basically stable.
Therefore, Liu Bang and Li Yuan, both in the final, patiently accumulated their strength first and finally killed the remaining opponents.