(1) Economic poverty. Reason: the tyranny of Qin and the destruction of long-term war [peasant war and Chu-Han war at the end of Qin Dynasty]. Solution: Emperor Gaozu learned the lesson of "sharing interest with the people" in the Qin Dynasty's death, and adopted measures such as thinning, heavy punishment, emphasizing agriculture and restraining business, etc. to increase agricultural labor force and mobilize farmers' enthusiasm for production; After Emperor Gaozu, several generations of emperors continued to carry out the policy of recuperation. By the time of Emperor Wu of the Han Dynasty, a large amount of grain and money had been accumulated in the national treasury, and the national strength was quite strong.

(2) Kingdom problem. The reasons are as follows: firstly, the dispersion of feudal economy made the nobles, bureaucrats and landlords within the ruling class have a certain degree of separatism, which is easy to form local separatist forces, which is the economic root of the kingdom problem; Second, in the early Han Dynasty, while eradicating the princes with different surnames, Liu Bang enfeoffed some children with the same surnames as local kings to ensure that the Liu family lived in the world. As a result, the influence of governors became more and more powerful, threatening the consolidation of the central government. The existence of feudal system is the direct cause of the kingdom problem. Solution: In the early Han Dynasty, Emperor Gaozu and Emperor Jingdi seized the kingdom fiefs and put down the "Seven Kingdoms Rebellion"; Emperor Wu of the Han Dynasty issued a "favor decree", and the kingdom became smaller and smaller. He also promulgated the "attached interest law" to limit the activities of governors; Implement "ousting a hundred schools of thought and respecting Confucianism alone" and strengthen ideological rule. The kingdom problem has been solved.

(3) Xiongnu threat. Causes: During the Qin and Han Dynasties, the northern Xiongnu formed a powerful slave country, and the Xiongnu continued to attack the south, threatening the security of the northern border counties of the Western Han Dynasty; However, the Western Han Dynasty was in economic distress and its national strength was limited, so it had to "kiss" with the Xiongnu. Solution: Wei Qing and Huo Qubing fought three wars with the Xiongnu when they launched a military counterattack. Xiongnu was forced to move the capital to Mobei, and the northern border county of the Western Han Dynasty was decided.