Can't help but look at the density of regions like India and think it will brew trouble. I wonder what the correlation is between population density and violence, I imagine quite strong.
There's no correlation: Singapore and HK have some of the highest population density in the world, and have a low crime rate. Checking the list of countries by density[1] and then by violent crimes[2] will confirm that. India is quite violent, but for different reasons.
It's not violent like countries caught in the drug wars, but a single number fails to give the whole picture: in India a lot of the violence is targeting lower castes and religious minorities (Muslims, Christians, Sikhs)[1], sometimes with the (more or less overt) approval of the current ruling party (BJP -- Hindu nationalists). A recent shocking example is the gang rape and murder of an 8 year old Muslim girl: although most of the country was horrified by this, some of the demonstrations were in favour of the accused, and for the charges to be dropped[2].
So yes, when the ruling party basically deliberately targets minorities, I would qualify that country as "quite violent".
In all fairness, back in the old days, you really had to watch your step in HK. It had more than its fair share of crime. Far more. But this was in the 80's and early 90's.
They had an anti-crime and anti-corruption campaign, and of course there was the handover. So obviously crime dissipated as a result. But it was really bad in the old days.
I don't really know much about Singapore. I've never been there. That said, if crime is low, I'd imagine there were, at least for a time, exceedingly strict punishments for lawbreakers given the population density.
You are correct about HK (in fact I think the higher crime rate was much older that just the 80s and dated back to the 50s and mass emigration caused by the successive troubles in the mainland). I do think it's a great story, as it demonstrates an administration can completely turn around a police force from utter corrupt to highly professional in around a decade. In Western countries where the worldview is often 'static' it's also a good reminder that societies can change quickly.
And yes in Singapore the laws (and their enforcement) are much more strict.
Hong Kong started phasing out leaded gas around 1992; so you would expect a drop in crime rates about 2004 or so. And of course that's exactly what the statistics show.
[1] https://en.wikipedia.org/wiki/List_of_countries_by_populatio...
[2] https://en.wikipedia.org/wiki/List_of_countries_by_intention...