No, other rich countries didn't solve this problem because other rich countries never had this problem. America has always had lots of guns but it didn't always have lots of mass shootings. We're 5% of the world's population and we own
50% of the guns in the world.
This specific problem? Sure. That's sorta what happens when problems weren't nipped in the bud, though, and are allowed to progressively get worse and worse.
It's going to take more than simply passing laws that make "weapons of war" and "assault rifles" illegal.
Duh?
I haven't seen any specific proposals to reduce gun violence that aren't so broad as to be meaningless.

There's a difference between a general platform/push for action in a particular direction and the specifics, certainly. Are you seriously demanding that the MSD students, who you've been attacking like crazy, should be supplying all the minutia? Going past that, a number of the suggestions are actually quite specific, really, so your standards for broad seem utterly meaningless.
The talking points on the Marchforourlives website and the MSD student manifesto that have been referenced in this thread have a few suggestions that are worth discussing. But they're buried in simplistic hysterics.
Then actually address such and a more interesting discussion can be had on the pros and cons of particular points than all these attempts to poison the well, fight strawmen, and employ ad hominems. You've seem to have been being too busy bashing on the people and making yourself look incredibly ignorant or irrational about nearly everything related to the topic instead of doing so, though.
The fact that these are considered reasonable actionable suggestions by a majority of people makes me very pessimistic about the ability to actually solve the problem.
Some are quite reasonable, some are rather so less than the others. Of course, then there's what you mean by "solve the problem." The perfect solution fallacy is a terrible defense, as are many of the other dodges that you've tried to employ.
The MSD manifesto is particularly depressing because these teenagers are calling for changes that are really not much more than making Federal law conform to California's gun control laws. The problem is that the MSD shooting isn't a failure of gun control.
Correction: It would be far more accurate to say that it's not solely a failure caused by the anti-regulation and get more guns into hands of everyone lobbyists.
It's a systemic failure that allowed a kid who law enforcement and social services had responded to something like thirty nine times and who was known to be violent was never flagged in any way as somebody who shouldn't be able to buy a gun.
Pretty much everyone agrees that it was a systemic failure, but those who disagree with you seem to think that it was a more extensive systemic failure than you clearly want to narrow it down to, generally because this isn't even remotely an isolated event. How many school shootings have there been this year, alone, again?
Universal background checks and mental health databases are worthless if violent psychos aren't entered into them.
Sure. Of course, that's skipping over the fact that there's lots of information of relevance that
is entered somewhere but doesn't get to the UBCs, frequently as a result of the pro-gun lobbyists' actions. You're trying to focus on nebulous gross incompetence of individuals, while ignoring the actual suggestions regarding gaping holes in the system itself, by the look of it.
It's understandable why David Hogg and Sheriff Scott Israel want to smear the NRA rather than look at the failures of law enforcement. But if the
policies adopted by an out of control PC culture have created a milieu in which we worry about a kid named "Cruz" being stigmatized by being arrested or held for psychiatric observation, we should look at changing those policies. Problems aren't solved by blaming the wrong people.
They aren't solved by simply ignoring important factors, sure. Unfortunately, the simple fact is that it gets really, really hard to put much faith in the opinions of people who really need to take heed to the admonition "Why do you see the speck that is in your brother's eye, but do not notice the log that is in your own eye? Or how can you say to your brother, ‘Let me take the speck out of your eye,’ when there is the log in your own eye? You hypocrite, first take the log out of your own eye, and then you will see clearly to take the speck out of your brother's eye."