A common context for an escalation of violence toward homicide is two strange men in a public place arguing over a woman. Maybe one is the boyfriend or husband, and maybe neither is but both are interested in her. Words and stares are exchanged, each feels pressure from the woman and the public not to back down, and suddenly they're off on a trajectory that could end in death.
The woman is not just a passive bystander. In some way she allows or provokes the advances from Guy #2, regardless of whether or not Guy #1 was her boyfriend or husband. Guy #2 comes over to talk to her, and she doesn't brush him off, shoot him a cold or confused look, etc. She likes having men compete for her attention (leveling up her ego points), and she may also want to keep her sexual options open. So she is at least not put off by Guy #2, and may even turn toward him, engage him in conversation, laugh, smile, and so on.
The sense that Guy #1 could lose access to something he had expected to be his -- either his girlfriend / wife, or a strange woman who he had "dibs" on by engaging her first -- leads him to cut off the external threat. He hoped that she'd just give Guy #2 the cold shoulder, and that would be that. But dangit if she isn't turning toward him, smiling and talking. He will have to drive off the rival by himself (or with the help of his buddies).
These initial steps in the escalation toward violence do not take place when the woman is cold, brusque, and unwelcoming to strange men. Guy #2 leaves on his own because he got the hint that she couldn't be less interested in him. That saves Guy #1 the risky task of regaining sole access (at least in the near term) over what he believes to be his, against a motivated male rival. In fact, after getting the cold shoulder, Guy #2 is not motivated at all.
I think these differences in average female dating-and-mating behavior go a long way to explain differences in violence among males of one group vs. another. Rude and frigid Yankee women are unlikely to allow, let alone encourage, two or more men to literally fight over her affections. "Is that guy seriously coming over to talk to me when my boyfriend's right here? How bitchy should I sound when I tell him to 'Find someone else to tell your lame lines to, creep'?"
These women have low sex drives, and use sex as a bargaining chip to get a high-status man to settle down and invest in her and her offspring. She would never entertain thoughts of "Hey, another lover... y'know, just in case," or "Hey, I wonder if he'd be a higher-quality stud... might be only one way to find out for sure."
Hence, Yankee men still compete for access to this woman, but it is not over who can get her the most hot and bothered, or who's man enough to displace the other one from a public place, in front of a public crowd. Rather, it's who can strive for the highest status and offer her the greatest material and reputational gains if she agreed to dole out sex on a regular basis.
Those Southern women, on the other hand, are frisky little kitties. They like keeping their options open (without appearing brazen -- more like having a wandering eye), having multiple suitors fighting over them, and surrendering to the moment. "In the heat of passion" describes not only her momentary lapse of fidelity, but also Guy #1's resort to violence to punish her and Guy #2 when he catches them.
There isn't much heat of passion up in Minnesota, so they don't have to worry about dangerous situations like these.
Comparing two groups is a suggestive but weak way to establish causation. Looking at how a group changes over time is better. As the causal variable changes, the response variable out to, well, respond.
Frisky females seem to be part of the outgoing phase, and frigid females part of the cocooning phase of the cycle of social openness and interaction. You can see young women getting a little more out-and-about by the mid-to-late '50s, for example by joining guys in public hang-outs, which are usually felt to be "creepy" places if the girls are frigid and cocooning. Swooning over Elvis was way more scandalous than having a crush on Frank Sinatra. And the incidence of common venereal diseases had begun rising already by the late '50s.
The homicide rate didn't start increasing until 1959, and other violent crimes in the early '60s. This argues against the view that frisky female behavior is a response to male violence, but is rather a contributing factor to it.
Of course, that isn't the only or even the primary cause of rising homicide rates. As far as the cocooning vs. outgoing behaviors go, I think simply having a lot more people out in public, and with their guard down / trust up, is what drives crime rates up. Criminals find easy pickin's in such an environment, and are left with little to do when everyone is locked inside their nuclear household as they were for much of the mid-century and the Millennial eras.
We should not greet this as good news -- "My daughter won't get knocked up, AND crime rates are plummeting? What's not to like?!" That has come at the cost of complete social isolation. That's why they're not dating -- minimal interest in boys and other people in general. Reality check: girls in the good old days were not sleeping with a different guy every week, and the homicide rate at its peak was around 1 in 10,000. You faced a higher risk of getting robbed then than now, but you didn't leave your house with a bullet-proof vest on.
Then again, how many people care about the "cost" of social isolation when most folks are cocooners? To them, that's just one more reward -- "No awkward interactions either?!"
This also explains why certain cultures used to be romanticized, while new ones are idealized today. It used to be Los Angeles, Dallas, and Miami. Now it's DC, Manhattan, and Brooklyn. It used to be the Mediterranean, now it's Scandinavia. That echoes who was prized by folks in the Jazz Age and the Mid-century, respectively. In outgoing times, our attention is drawn to more hot-blooded cultures.