Would this have happened if guns were banned in the US?
Yes - if the ban wasn't enforced and the penalties for those actually prosecuted were zilch - which is pretty much the case here.
I'll give you an example or two and then the opposing views on what makes sense.
In Arizona, you can buy 50 AR-15 assault rifles and ten minutes later, sell them to a guy who has been convicted of murder - as long as you don't ask him about it and therefore, don't know he is a convicted murderer.
In Los Angeles, police can pull over a known member of the Crips, Bloods or other gang - find him wearing a wig and disguise and carrying an illegally purchased gun. As long as he hasn't been convicted of a felony yet, he'll plea bargain out in an hour because he hasn't actually killed somone... yet.
As long as you can pass the background check one time, you can become an arms dealer without owning a store or anything. You have less than a 1% chance of ever being investigated. Then you can sell pistols, sniper rifles, assault rifles, silencers (ecause you know, that's so necessary for defense) and whatever. Do these people sell guns illegally? Duh.
So it's not a matter of laws. It's a matter of enforcement.
Extreme Liberals have a solution to America's Gun Violence Problem: They want to ban all guns but they are fairly rare.
Moderate LibDems, Moderates and Indies Liberals have a solution to America's Gun Violence Problem: They think gun ownershio is fine but carrying machine guns into the kindergarten or better yet, the bar where you go get drunk, is just plain foolish. I agree. I own a gun but don't take it to the movies or anywhere in the city. It's at home.
Conservatives Liberals have a solution to America's Gun Violence Problem: More guns. I'm not kidding. Oh and less laws. If our laws and their enforcement is too weak now, the solution is to make even less of them. You'll hear cute little chants they've been taught like "If guns are illegal only criminals wil have guns." Well duh. And if child porn is illegal, only criminals will have child porn. So should we make it legal? The anti-logic of this is almost amusing. Oh well. They really do buy it.
My favorite one is when they compare gun ownership to owning a car. Unreal.