Consider this chart:
As you can see, since 1976 there's been a marked decline in the number of men murdered by their wives in the United States and a smaller, but still significant, decrease in the number of women killed by their husbands. The graph comes from Sociological Images where Jay Livingston asks for suggestions that might explain this trend. He suggests that perhaps men are behaving better (not a popular theory, I'm going to guess) and that women have more options, citing the work of women's shelters and the like in making it easier for women to escape abusive situations without murdering their spouse.
Matt Yglesias says, however, that what needs to be explained is the US's previous " unusually low level of gender inequality in intimate homicide"; Kevin Drum, on the other hand, suggests that improved 911, trauma and medical care may have something to do with this.
The data from which Livingston has created this graph is, incidentally, available here. So, a theory? Well, the first thing to note is that it has become vastly more acceptable to report crimes of domestic violence - physical and sexual - than it was in the 1970s. This in turn must have a) put behind bars some men who would otherwise have been candidates to be murdered by their wife or to murder her themselves and b) done so before a final, fatal confrontation.
Secondly, changing attitudes towards marriage and the destigmatisation of divorce. In some areas this has been an unfortunate devlopment or one, rather in which there are some negative trade-offs to be considered even as one also remembers the advantages of such a trend. A decline in intimate murder seems to be one of those happier trends. I'd like to see how changes in the acceptability of divorce - especially divorces instigated by the woman in question - mapped with the geographical distribution of intimate homicide. Surely it's possible that changes in attitudes towards divorce, especially in the south of the United States, might be the most important thing?
As against that, there's also been a sharp drop in the number of African-American men killed by their wives and girlfriends. In fact, the intimate homicide rate for black husbands and ex-husbands was twenty times greater in 1976 than it was in 2005. My guess would be that the breakdown of the black family in inner-city America has something to do with this. Abandoned wives may be resentful, but they're hard-pressed to murder a husband who is never there. For that matter, the War on Drugs may have a part to play too since, again, an imprisoned man is not in a position to murder, or be murdered by, his wife. This, then, might be the one area in which the War on Drugs actually might save lives...
On Yglesias's point: I'd guess that the low level of gender divergence in the US has something to do with the availability of weapons. Though roughly 25% of men murdered by their wives are stabbed to death, the majority of such victims are shot. The greater availability of guns in American households - even if most of those weapons would be owned by men - made it easier, surely, for American women to murder their husbands. In other countries, lower levels of gun ownership impact the range of weapons avaialable to women and, crucially, the amount of physical power they need to achieve their goal. American women may have had more accessible and easier to use equipment than their battered counterparts in other countries.
But, I dunno, what do you guys think?