One thing that dictates why the US is so different is the Geography. It's huge, with people living all over (something Canada doesn't have as bad). And let's say in the UK, it's easier to control a more densely populated country, so much so the police don't need guns. #
Regarding poverty, the fact is Europe has social housing for all and I have noticed that the amount of homelessness in the US is relatively high compared. I'm guessing this goes back to certain policies and some cultural things (like how socialism is frowned upon in the States while in Europe it's part of the fabric of society).