How did blood feuds arise after killings and robberies between family groups?

In the context of Germanic law, blood feuds arose as a mechanism for redress when offenses—specifically open killings and open robberies—occurred between members of different family groups, or clans.1

Because these societies relied on collective solidarity, an injury to one individual was viewed as an injury to their entire kinship group, or sib (sippe). When such a grievance occurred, the victim's family sought revenge or honor through a feud, which involved a cycle of violence and counter-violence.12

To prevent these hostilities, societies often utilized blood money, known as wergild for homicides and bot for other damages. While initially voluntary, these payments allowed families to "buy peace" and avoid the escalation of a feud. If the parties could not reach an agreement on compensation, the state of conflict would continue. These private feuds were eventually curtailed as royal authority grew and legal systems shifted toward formal judicial processes.341