I found this explanation of the general evolution of stand your ground on a criminal law website:
DUTY TO RETREAT
English Common Law required that an individual, when threatened, must "retreat to the wall at one's back" before justifiably killing someone. Only the crown could kill someone and justify it. Everyone else had to get a pardon from the king if they killed someone. The only way to do that was to prove that you did everything you could not to kill someone.
"private persons are not to be trusted to take capital revenge one of another." - Sir Matthew Hale, Jurist
This English Common Law became America's Common Law and is the starting point for all self defense laws to follow.
CASTLE DOCTRINE
Castle Doctrine is another English Common Law adopted in America to remove people from the "duty to retreat" when attacked in their own home. Every state supports the Castle Doctrine through legislation, case law, or common law.
"A man's house is his castle -- et domus sua cuique est tutissimum refugium" (and where shall a man be safe if it be not in his own house?) -Sir Edwar Coke, The Institutes of the Laws of England, 1628.
Everywhere else, one must try to retreat when threatened if it is safe to do so, before committing to killing someone in self defense.
STAND YOUR GROUND
Stand Your Ground laws are renovations to the Castle Doctrines already found in the states. In fact, they are often called Castle Doctrine Expansions. They are also called 'Shoot First', 'The Right to Commit' Murder', 'Line in the Sand', and 'Make My Day' laws.
These are laws that extend the castle doctrine in several different ways:
Location - Nobody has ever had to retreat when threatened in the home. SYG laws remove the 'duty to retreat' from outside the home as well.
Presumption - Justifiable homicide requires a 'reasonable belief' that a serious threat has been posed, and the threat must be 'imminent'. SYG laws presume that the surviving party had 'reasonable belief' or that the threat was 'imminent' or simply that the survivor killed legally in self defense. In other words, it's up to the non-survivor's party to prove otherwise.
Immunity - Generally speaking, criminal law punishes wrongdoers, and civil law attempts to restore what was damaged to whoever has been wronged. SYG laws give the survivor immunity from civil law suits and sometimes criminal law suits and even arrest.
Threat - Some states don't require there to be a 'reasonable belief' that a serious threat has been posed or that the danger be 'imminent'.