That's an opinion claiming to be a fact.
[0] http://en.wikipedia.org/wiki/File:Chicago_violent_crime_map_...
Um, can you give a source on that? I rather doubt it's true, but probably depends on what you mean by "most dangerous". (And also perhaps "developed").
Here's an article titled "Violent crime worse in Britain than in US": http://www.dailymail.co.uk/news/article-25671/Violent-crime-...
Or here's PolitiFact:
> For England and Wales, we added together three crime categories: "violence against the person, with injury," "most serious sexual crime," and "robbery." This produced a rate of 775 violent crimes per 100,000 people.
> For the United States, we used the FBI’s four standard categories for violent crime that Bier cited. We came up with a rate of 383 violent crimes per 100,000 people.
[Source: http://www.politifact.com/truth-o-meter/statements/2013/jun/... ]
Already you can see that adding up those categories doesn't make sense as some will overlap (in particular violence and the other two).