What determines the homicide rate variation across countries?

From the article: Cole J., Marroquin A., 2009. Homicide Rates in a Cross-Section of Countries: Evidence and Interpretations. Population and Development Review 35, 749-776:

• Latin America tend to have homicide rates that are, on average, roughly twice as high as those in similar countries located outside this region (e0.7133 = 2.041). 

• An increase in the ELF (Ethnolinguistic Fractionalization Index) from 0 to 1 (i.e., the difference between a totally homogeneous population and a totally fragmented one) implies a roughly 250 per cent increase in the average homicide rate (e1.2607 = 3.528). 

• Other things equal, an increase of one year in the average level of male schooling reduces the homicide rate by about 29 percent . . .  

• A one point increase in the World Governance Index reduces the average homicide rate by about 74 percent. The WGI is defined over a range from –2.5 to +2.5, with countries with “average” governance having a rating of 0. Therefore, other things equal, countries at the extreme low end of this range (worst possible governance) would be expected to have a homicide rate about 6 times higher than a country with “average” governance (e–0.7377•(–2.5) = 6.323), while a country at the high end of this range (best possible governance) would have a homicide rate about 6 times lower than a country with average governance (e–0.7377•2.5 = 1/6.323 = 0.158).