Who is harmed by a homicide? Certainly the individual who loses their life is harmed, but who else? Any family that is connected to the individual or depends on them is harmed, but beyond that, one can argue that the entire society to which the individual lived is harmed. If you take this broader view, then it makes sense that the crime of homicide could be an offense against the state, and not just an offense against a single individual or their close family.
In The Better Angels of Our Nature, Steven Pinker thinks about what this shift in perspective regarding the crime of homicide means for violence between and amongst human beings. He writes, “for centuries the legal system had treated homicide as a tort: in lieu of vengeance, the victim’s family would demand a payment from the killer’s family… . King Henry I redefined homicide as an offense against the state and its metonym, the crown.” When murder shifted from an offense against an individual or their family to an offense against the state, the potential rewards from murder dissipated. A single family could only do so much to seek retribution from a murder. And if the killer was big enough, strong enough, and influential enough in the local community, there was no chance that the family could ever seek justice. Murder was a path to riches, to status, and to power when it was only a crime against a single family or person.
The state, however, had more power, resources, and authority than any local individual. There may have been some individuals with extreme power and the ability to get away with murder, but shifting homicide to an offense against the state reduced the number of individuals who could kill without regard for consequences. Murder, for most, no longer existed as a good pathway toward greater riches. Shifting the offense shifted incentives and encouraged greater civility, reducing violence. The state, and its justice system, created an institution to reduce violence where previous institutions encouraged violence.