The 2010 census shows Asians accounted for around 45% of the city's population then and likely the majority now.
Having said that, one can't ignore that Japan is ethnically homogenous and geographically isolated. That makes it much easier to run a society. The pressure to be "proper" (in behavior and life) also causes a lot of depression and suicide (as the numbers show). But still, it's my favorite place I've ever been. I can't wait to go back.
Japan and Korea share many characteristics, and one of them is low crime and murder rates. One reason in Korea is cctv cameras EVERYWHERE. Also constant watching by others in person.
I think also the suppression of losing one's temper is considered admirable (although Koreans are hot-tempered) so blustering in a bar fight and brandishing a weapon would be OTT here, unlike in the US.
Of course, you can have a peaceful, non-polarized societies that are culturally diverse too. As wkrpync said above, many of the American cities with the largest immigrant populations (New York, Los Angeles, El Paso) tend to have relatively low murder rates compared to the rest of the population.
Regardless of the possible influence of homogeneity on crime though, the biggest factor behind high crime rates in America are lax gun laws (see my comments below).
The most obvious correlation when looking at this list, plus the extra statistics provided would appear to be poverty. But Mississippi doesn’t appear, which suggests that, as with most things, multiple factors are probably at play and there isn’t a single, simple explanation. But at least we can probably dismiss one simple explanation- can’t blame immigrants for this one.
What actually does show more of an impact than anything else is reduced lead exposure - this exposure is known to not only harm intellectual development, but result in more violent tendencies. As we've eliminated leaded gas and leaded paint, lead exposure levels have plummeted, followed by perfectly correlated declines in violent crime rates, delayed by 15-20 years (ie, the time it takes for kids to grow up).
Unfortunately, many poverty-stricken areas never have had good lead paint removal programs. We'd rather spend a fortune to incarcerate them than to fix the problem on the cheap.
Gun ownership IS directly linked to violence in America. Studies such as this one show the link pretty clearly. Sure it doesn't determine causation, but there's still a pretty strong correlation. In terms of developed Western countries, no one comes close to America's firearm-related death rate.
It's not just a homicide or mass shooting problem either--most suicides in America are committed using firearms, and so gun control would likely cause significant decreases in suicide.
I'm not saying guns are the *only* factor leading to violence in America (as jmellor nicely explains), but it's still absurd to think that guns are not a problem in America.
Often people hear the news headlines and miss the underlying facts. For example, the city of Detroit is only roughly 1/6th of the total population of Metro Detroit. So they hear about high murder rates in Detroit and conflate that with high murder rates around the entire metro region, when most of it is in fact very safe.
Or they hear about high numbers of murders in Chicago and assume its a complete war zone, when in fact many cities in the US have equally high or higher murder rates (St. Louis, Baltimore, New Orleans, Cincinnati, Cleveland, etc)...
Obviously not the ONLY factor but could be a social indicator?