Compared to all of them. Most are developing, yes, absolutely. When I started looking into it, I was surprised to find out that you're more likely to be murdered with a gun in Italy (66.7%) than you are in America (60%) even though Italy has basically the same gun laws as Canada (32%). Brazil's is 70.8% and they have more restrictive gun laws than any of the 3 previously mentioned. Source:
Gun homicides and gun ownership listed by country | News | The Guardian It is worth mentioning that in Canada they implemented stricter laws than they currently have then repealed them when they found that it was a nuisance for law abiding firearms owners, but didn't have any effect on the use of firearms in crime.
Like I said, America certainly has a serious murder problem. They also have a lot of systemic issues (like piss poor social support systems) that enable it to take place because they do nothing to address it. They have the global economy of a developed country, but all the problems of a third world one. Even if you took every firearm away from Americans you'd have the same issue, they'd just be using knives, or whatever else was available. I can promise you, the guy that wrote a 32 page letter about how society screwed him, that he was a powder keg, and how he was taking "inspiration" from other mass murders; wouldn't have said "Oh, man. I don't have a gun, guess I'll play X box instead"
I'd be curious to know, what period of civilization would you take us to where humans weren't killing each other for no reason? It's humans that are the problem, not the tools they use to kill each other. We've found different ones to use since day one, and will continue to do so.