Why did Wang Mang kill his son? In ancient China, the vicious incidents of fathers killing sons and sons killing fathers mostly occurred in the royal family. The number of emperors who killed their sons was a very small number for a long time. Although Emperor Wu of Han, provoked by the traitor Jiang Chong, killed his son and three grandsons, he later regretted it. And Wang Mang's forcing his own son to commit suicide seems to be addictive, even in the fratricidal royal family, it is very special.
Wang Mang's second son, Wang Mang, was killed by a slave, and Wang Mang severely rebuked him and forced him to commit suicide. In that era, killing slaves did not require life, so some people sang an ode to Wang Mang in this way, thinking that Wang Mang had a humane spirit.
Before evaluating this matter, it seems that Wang Mang forced his own son to commit suicide seems to be only a matter of indifference. Of his four concubines, all but one died of illness, and the other three were forced to commit suicide by him.

First, forced to kill the second son Wang Yu
The first person to be forced to die by Wang Mang was his second son, Wang Yue, ostensibly because Wang Yue killed his slaves. During this period, he was forced to leave the capital due to the exclusion of Emperor Wu's foreign relatives Fu and Ding. Is the death of the son due to a problem with the father-son relationship? Or is it because of the loss of power to lose power and to be angry with his son? Or do you want to make a comeback with a false name? Don't dare to assert it. However, it is certain that he is not fighting for the humanity of the slave, otherwise when he is in power, even if he does not abolish the slave system, he can issue decrees that guarantee the minimum rights of the slave (such as the right to life), or release some of his own slaves as an example. None of this, so it makes no sense to say that he sympathizes with the slave.
This happened in the first year of Emperor Wu's reign (2 BC) or earlier. Wang Mang was excluded from Beijing for three years, during which time he wrote to the emperor about Wang Mang's wrongs in being excluded from Beijing and praising Wang Mang's merits, and the only thing he could afford to show during his absence from Beijing was to force the killing of his second son.
Second, forced to kill the eldest son Wang Yu
After Emperor Wu's death, Wang Mang made the nine-year-old King of Zhongshan emperor, and in order to prevent Emperor Ping's mother from fighting for power with him, he was not allowed to include Emperor Ping's mother Wei Ji to come to the capital, and Emperor Ping's uncles were all marquises, but they were also not allowed to come to the capital, and no one of the Wei clans was allowed to come to Beijing. Wei Ji wanted to see her son cry day and night. Wang Mang's eldest son, Wang Yu, feared that Emperor Ping would take revenge on the Wang clan when he became an adult, opposed the isolation of the Wei clan, and contacted the Wei family to oppose Wang Mang's actions. He knew that persuasion was useless, and wanted to intimidate Wang Mang with a ghost god, and sent his brother-in-law to sprinkle blood in front of Wang Mang's door, and was discovered.
For this reason, Wang Mang forced his own son to commit suicide by drinking poison, and at the same time killed all the members of the Wei clan, leaving only the emperor's mother Wei Ji alone. This incident occurred in the third year of the first year of the Ping Emperor's reign (3 AD).
It seems that Wang Mang's eldest son's thinking is normal, he is considering the long-term interests of the Wang family, and wants to establish a relationship with the Wei family for the future. At this time, Wang Mang should have already had a plan to seize the throne, otherwise he would not dare to persecute the Wei family in this way, let alone use his son's affair to destroy the Wei family.
It can be concluded that such a plan existed only in Wang Mang's own heart, and no one knew about it, at least his eldest son, who may be the future crown prince.
Forcing the eldest son to be killed may be to pave the way for the elimination of the Wei clan, but it is also too fierce.
Third, force the killing of the young son Wang Lin
The eldest son, the second son, was forced to commit suicide, while the third son, Wang An Buqi ("An Po Huang"),the youngest son, Wang Lin, was made crown prince when Wang Mang was emperor.
When Wang Lin saw that his two older brothers had been forced to die at the age of thirty, and that he himself was thirty years old, he couldn't help but feel uneasy in his heart, not knowing how he would die. Wang Mang's wife was blinded by wang mang's crying because wang mang forced her son to die, and when Wang Mang's wife was seriously ill, Wang Lin revealed this meaning in a letter to his mother, and wang mang saw it and was furious, thinking that Wang Mang had malicious intentions.
After the death of Wang Mang's wife, Wang Mangxing was poorly cured of some things, and found that when Wang Lin was serving his sick mother, he had committed adultery with Yuan Bi, a beautiful maid beside Wang Mang's wife, and Yuan Biben and Wang Mang also had an adulterous affair. The results of the interrogation of Yuan Bi found that Wang Lin, fearing that Wang Mang would find out about the adultery, had the intention of conspiring with Yuan Bi to murder Wang Mang (is it true?). Or was he forced out by heavy torture? I don't know. ).
Wang Mang gave Wang Lin the poisonous wine, which he did not drink, stabbed himself to death. This incident occurred in the second year of Wang Mangdi's reign (21 AD), two years before Wang Mang was killed in defeat as emperor.
Another son, Wang An, fell ill and died. Wang Mang's concubines were all dead. Therefore, Wang Mang brought Wang Xing and Wang Kuang, the sons of Wang Xing and Wang Kuang, who were originally secretive, and brought them to the capital.
Wang Mang is not addicted to forcing his son to die, he has this habit, and he does not dare to assert, but, it may be certain, Wang Mang is also like a cold-blooded animal to his recent blood relatives, forcing his son to commit suicide is just a piece of cake.
Perhaps, from the perspective of human nature, Wang Mang's forcing his son to commit suicide is the most incomprehensible, because his son's actions are far from threatening him. As long as you communicate with your son, you should not end up with death.