Just an example of how long Americans have been debating whether there should be a “duty to retreat” before using deadly force in self-defense, from Commonwealth v. Selfridge (Mass. 1806), sometimes described as the first American case to deal extensively with self-defense:
A man may repel force by force in defense of his person, against any one who manifestly intends or endeavors by violence or surprise, feloniously to kill him. And he is not obliged to retreat, but he may pursue his adversary until he has secured himself from all danger; and if he kill him in so doing, it is justifiable self-defence.
2. Now from Justice Isaac Parker’s charge to the trial jury:
A man, who in the lawful pursuit of his business, is attacked by another, under circumstances which denote an intention to take away his life, or do him some enormous bodily harm, may lawfully kill the assailant, provided he use all the means in his power, otherwise, to save his own life, or prevent the intended harm — such as retreating as far as he can, or disabling his adversary, without killing him if it be in his power.
And Justice Parker assures the jurors that this proposition is not “contested anywhere,” even though it’s inconsistent with Chief Justice Parsons’ views (and Justice Parker was apparently present at the grand jury charge).
As best I can tell, the more or less orthodox rule during that era was the one set forth by Blackstone (and other writers). Homicide in order to prevent an unprovoked felonious attack — a murder, rape, robbery, and so on — was labeled “justifiable,” and allowed even if the defendant could have retreated. Homicide in a brawl that started as a nonfelonious battery (or perhaps even as a consensual fight) but that turned life-threatening was labeled “excusable,” and was excused only if the defendant couldn’t have reasonably retreated. But this is not the distinction between Parsons’ and Parker’s charges, because both seemed to be describing justifiable homicide. The American controversy over the duty to retreat is an old one indeed.