Nero had Agrippina killed because he saw her as a threat to his power. She had been a major political figure in Rome for many years, and she had a lot of influence over her son. Nero feared that Agrippina would try to have him overthrown and take back power for herself.
The exact circumstances of Agrippina's death are not known for certain, but it is generally believed that she was poisoned. Some sources say that she was given a poisoned drink, while others say that she was injected with poison.
In either case, Agrippina died quickly and painlessly. She was found dead in her bedroom, and Nero made sure that her death was announced publicly so that everyone in Rome would know that he was the new emperor.
Agrippina's death was a significant turning point in Nero's reign. It marked the beginning of his descent into tyranny and madness. He became increasingly paranoid and violent, and he ordered the execution of many innocent people.
Agrippina's death also had a lasting impact on Roman politics. It showed that even the most powerful women in Rome were not safe from the whims of their husbands or sons. It also contributed to the decline of the Roman Empire, as it led to a period of political instability and violence.