One day, Liu Bang summoned Zhou Chang, the imperial master, and told him that he would be demoted. Zhou Chang was very sad after hearing this, and said to Liu Bang: "When the subject first started from His Majesty, Why did His Majesty abandon him in the middle of the way?" However, Liu Bang said that only he could do this, and Zhou Chang agreed to it.
Originally, Liu Bang wanted to send Zhou Chang to the State of Zhao to protect Liu Ruyi, which was equivalent to demotion. Zhou Chang wanted to follow Liu Bang, so he felt sad, but Liu Bang believed that only Zhou Chang could protect Liu Ruyi, so he pleaded with him in every way, and Zhou Chang had no choice but to agree.
Liu Bang wanted to make Liu Ruyi the crown prince, which was a well-known thing, and it was also obvious that Lü Hou wanted to harm Liu Ruyi. Liu Bang sent Zhou Chang to the State of Zhao, fearing that after his death, Lü Hou would persecute Liu Ruyi. But why did Liu Bang send Zhou Chang? Zhou Chang was a human subject, could he stop Empress Lü? I think that Liu Bang sent Zhou Chang for these reasons.

First, someone recommended
When Liu Bang made Liu Ruyi the King of Zhao, Liu Ruyi was only ten years old, and at this time Liu Bang began to worry that someone would kill Liu Ruyi in the future. He had been thinking about who should be sent to protect Liu Ruyi in order to prevent him from being killed. It just so happened that a person named Zhao Yao recommended a person for him.
Zhao Yao was a subordinate of Zhou Chang, and although he was young, he could be wise and resourceful. Someone said to Zhou Chang that he should promote Zhao Yao more, this person is a rare talent, and he will replace Zhou Chang's position in the future. Zhou Chang did not agree with this remark, he believed that Zhao Yao was still old, and his official position was not high, and it was unlikely that he would replace his position.
Not long after, Zhao Yao gained Liu Bang's trust, and when he saw that Liu Bang was sullen and unhappy, he asked him if he was upset, whether Lady Qi and Lü Hou were at odds, and That King Zhao was too young. Liu Bang saw that he was in his heart, so he asked him what advice he had. Therefore, Zhao Yao suggested that Liu Bang send a person of high moral standing to the Zhao kingdom to protect the King of Zhao, who must even be in awe of Empress Lü.
Liu Bang said that he had thought about it for a long time, but he had never thought of a suitable candidate, at which time Zhao Yao said: "Zhou Chang, the imperial master, is stoic and straight, and since Empress Lü, the crown prince and the ministers are all respected." Duchangke. Liu Bang thought that his words were reasonable, so he decided to send Zhou Chang forward, so there was the scene at the beginning of the article.
After Zhou Chang went to the Zhao Kingdom, the position of Imperial Master was vacant, and Liu Bang took the official seal and then carefully looked at Zhao Yao. Later, Liu Bang appointed Zhao Yao as the Imperial Grand Master, and later Zhao Yao made meritorious contributions in the war against Chen Feng, and Liu Bang made him the Marquis of Jiangyi.
Second, Liu Bang trusted Zhou Chang
When Liu Bang first raised an army, he defeated the sheriff of Surabaya County, and the Zhou Chang brothers began to follow him. In the uprising to overthrow the Qin Dynasty, the brothers Zhou Chang and Zhou Jiao made great contributions, and after Liu Bang became the King of Han, Zhou Chang was awarded the post of lieutenant, and Zhou Cao was made the Imperial Historian.
Later, while stationed in Xingyang City, Zhou Jiao was killed by Xiang Yu, and Zhou Chang replaced him as the Imperial Grand Master. After that, he followed Liu Bang in his southern conquests of the northern war, and after Liu Bang became emperor, Zhou Chang naturally became a founding hero and was given the title of Marquis of Fenyin. It can be seen from this that Zhou Chang was Liu Bang's brother in life and death, and Liu Bang can be said to have extreme trust in him.
Zhou Chang had followed Liu Bang for many years, knew his personality very well, and knew what he was worried about. Therefore, when Zhou Chang went to Zhao Guo, he must know how to protect Liu Ruyi. Coupled with the fact that Zhou Chang's prestige in the DPRK was very high, it was not so easy for some people to harm Liu Ruyi.
Third, Zhou Chang was kind to Lü Hou
Zhou Chang had a saying that when Liu Bang proposed that he wanted to make Liu Ruyi the crown prince, Lü Hou did not know what to do. The courtiers were all opposed, but they did not dare to be the first to stand up, and only Zhou Chang resolutely stood up. He said very angrily that Liu Bang's decision was wrong, and he could never accept this edict.
Zhou Chang originally had the problem of stuttering, and when he stumbled and said this sentence, Liu Bang immediately laughed out loud, and did not mention the matter of changing the crown prince at the moment. Lü Hou was anxious about this matter, and was quietly hiding in the East Wing to eavesdrop, and she saw Zhou Chang like this and was grateful to him.
Later, when Lü Hou saw Zhou Chang, her heart was very excited, and she immediately knelt down and thanked him: "Wei Jun, the prince is a few wastes." This means that if it were not for Zhou Chang, the prince would almost be deposed. Therefore, Lü Hou was very grateful to Zhou Chang, and for this reason, with Zhou Chang coming forward, Lü Hou did not dare to move Liu Ruyi at will.
The truth was also as Liu Bang expected, and later when Lü Hou came to power, she sent someone to summon King Zhao to Beijing, hoping to kill him in the palace. After Zhou Chang learned of this, he lied that King Zhao was ill and could not go. Lü Hou looked at Zhou Chang's face and did not count his crime of resisting the will.
Lü Hou feared Zhou Chang, so he sent someone to summon Zhou Chang to Beijing, explaining to him his hatred for Lady Qi and hoping that Zhou Chang would fulfill her. But Zhou Chang said that he had been entrusted by Liu Bang to protect King Zhao. Lü Hou had no choice but to take advantage of Zhou Chang's absence from Zhao Guo and send someone to quietly summon Liu Ruyi back.
Zhou Chang was absent, and the people of Zhao Guo had no idea, so Liu Ruyi had to enter Beijing on his orders. Liu Ying knew that Lü Hou was going to kill King Zhao, so she personally went to pick him up and take him back to the palace, and then let him eat and live with him. Unfortunately, Lü Hou still found an opportunity to poison Liu Ruyi, and then threw Lady Qi into the toilet.
After knowing that Liu Ruyi was killed, Zhou Chang always blamed himself, believing that he had failed Liu Bang's instructions and said that he was not ill. Lü Hou respected him and did not feel sorry for him. Zhou Chang had always felt deeply guilty and could not let go of the matter, and three years later, he died, and his son inherited the title.
In fact, I think that Liu Bang sent Zhou Chang to the Zhao Kingdom to protect Liu Ruyi, which was a very correct choice. With Zhou Chang present, Lü Hou really did not dare to blatantly deal with Liu Ruyi. It's just a pity that Lü Hou respected Zhou Chang no matter how much he respected him, and the latter was only a courtier, and his arms could not be twisted over his thighs.
Zhou Chang was able to protect Liu Ruyi for a while, but he could not protect him for a lifetime, and Liu Bang's decision was not the cure after all. Lü Hou's heart to deal with Lady Qi's mother and son was already decided, unless Liu Bang was reborn, no one could save the mother and son.
(References "History", "Book of Han")