The origin of self-defense in Anglo-America is believed to stem from the pollination by the Normans, subsequent to the Norman Conquest of England in 1066, of the Anglo-Saxon conception of the sanctity of life with more nuanced Continental ideas. Previously, any killing, even in self-defense, was culpable. Once the accused was found liable, regardless of blameworthiness, the remedy was either monetary compensation to, or personal vengeance wrought by, the victim's family. Over time, the personal injury nature of a homicide became a public crime against the king, a breach of the king's peace. Private vengeance and reparations gave way to public punishment and forfeiture of the accused's land and possessions to the crown.
Gradually, English jurists began to wrestle with the issue of the relevance of the circumstances of a killing. The promulgation of the Statute of Gloucester in 1278 allowed defendants who killed by accident or in self-defense to apply to the king for a pardon. By the beginning of the fourteenth century, justifiable homicide preserving the king's peace—the execution of a felon sentenced to death or one resisting capture—was distinguished from excusable homicide or se defendendo, for example, in self-defense. In 1532, King Henry VIII's parliament enacted a statute that eliminated the forfeiture of property. In 1769, Blackstone explained that justifiable homicide could only be killings required by law that promoted the social good. Personal killings in self-defense could only be excused because they could not be absolutely free from guilt. In excusable homicide, the accused had to retreat to "the wall" before killing (except if he was in his "castle") but in justifiable homicide the accused need not retreat and could even pursue the felon.
Blackstone's interpretation was imported into the New World and became quite influential, indeed it was often the only source of law. As the frontier expanded westward, however, sentiment grew that retreat before using force in the face of a wrongful assault was cowardly and unmanly and gradually the retreat requirement dissolved. (Cynthia Gillespie contends that this male perspective infuses present self-defense law to the detriment of women.) Even today, while eastern states generally retain some form of retreat requirement, most western states do not. Gradually, self-defense became justified even though it did not further the public good in Blackstone's sense.
Law Library - American Law and Legal InformationCrime and Criminal LawJustification: Self-Defense - History, Theories, Modern Law, Reasonableness, Necessary Force, Deadly Force And The Duty To Retreat