Japan's high degree of order works because everybody is culturally on the same page. If you throw trash on the ground, 100% of the people around you will give you a disapproving look.
Inject millions of immigrants into their society to upset their homogeneous cultural order and I bet the police would be a lot more busy.
The interesting thing about Japan is the poverty level is estimated to be relatively high. In general we see that crime scales with poverty, but not as much there. That should be subject to more research.
Seems to me the stabilizing effect of a stagnating population is the main reason.
History will ultimately be the judge, but I truly worry about the sustainability of many things in the US.
I grew up in a rural area of New York, which is basically rotting away. I worked on a farm as a kid that was continuously operated since the 1680s that is suddenly not viable.
Life is great for my family, thanks to good education, luck, and good decisions, but I worry about my kids’ future.
I would wager if Japan allowed as many El Salvadorians into Japan as made it into the US, they would start having MS-13 problems too (but maybe not; Japan authorities pretty much decimated the Yakuza last I read).
[1]NSFW Google search: "site:tokyoreporter.com yakuza". TokyoReporter is my favorite English-language Japan news source; they cover all the seedy shit like ex-porn stars getting busted for drugs.
United States 13.7%
Sweden 18.5% [born outside the EU: ~14%]
http://buzz-plus.com/article/2018/10/29/garbage-shibuya-hall...