Honestly...
depends on how close you stack 'em...
the correlation 'tween violence and stressed (unnatural) urban environments with little to no interaction with nature, coupled with stacking and cramming people in small areas will always result in an eventual negative impact on the inhabiting individuals...same goes for alot of other species.
We are after all an animal...affected and developed by environmental circumstance.

Ideologically...the same applies.
Take flavours political.
Now mix in the ingredients...
A- those nations WITH moderate to abundant valuable natural resource ...tend to have gov't that is moderate, socialistic and/ or capitalistic...with a relatively peaceful population...the gov't CAN afford to be benevolent.
B- those nations with little to no valuable natural resource..tend to have gov't that is militant, religious or dictatorial...because there is little to go around it is policed. Likewise violence and ignorance are perpetrated and instilled in the population...since it is easier to subjugate and rule an uneducated populace. Also public unrest is wont to be high with a population that has less freedom, personal wealth and fear and uncertainty concerning the future for themselves and others. ...the gov't CANNOT afford to be benevolent..peace, order and rule of law must be maintained.

Machiavelli is correct...and then some.
Where he wrote on the methods of rule...
The "why this way...and not that way..." ...is intriguing ...