And you say Japan is monoethnic and rich and all, so it is reasonable that the entire 120 million people island have less murders than Alabama (with their 5M people).
OK, let's take a poor country, struggling with high unemployment, low salaries, 10% of the people walking on the street being immigrants and refugees from the Arab Spring (half of them illegal): Greece!
Greece is the size of Ohio in population and land size. GDP per capita is about 21000$ and we are below average on many many economic indices (14.5% unemployment). We also have strict gun controls.
Ohio has the equivalent of GDP per capita of 60000$, about triple that of Greece. Ohio has 4% Unemployment, 10% and 4 times below Greece.
Poor, multi-ethnic Greece has like 70-90 murders per year. Rich Ohio has x10 as many with the same population.
Q.E.D