Every country has its violent types, but mass shootings for no clear reason other than shallow disaffection seems unique to the USA. They are extremely rare even in notionally similarly rich countries allowing private gun-ownership.
Such as Switzerland where holding guns at home was part of a military conscription / reservist system it scrapped only quite recently. Or France and Malta, with many so-called "hunters" who love to blast away with shotguns at flocks of migrating birds as "sport" - not even for food. Some people in rural Norway shoot wild elk, for their meat - but to limited, licenced numbers.
In the UK, gun ownership is far less common because very few Britons feel they need, want or can justify a gun. The nearest, other than agricultural pest-control and collecting antiques that cannot be fired, are the sports of clay-pigeon and game-bird shooting. Both are under very strict controls, but those birds are edible and most are bred for it. (Plenty of Britons would like that stopped altogether.) Even so, occasional Police gun amnesties net a surprising number and variety of weapons. Many are war "souvenirs" or sports guns left by deceased owners, or are legally-held but handed in as no longer wanted. One Police Force donates the hardwood parts from the stocks of the guns it destroys, to a "Men In Sheds" scheme!
The least privately-armed of the developed nations appears to be Japan.
In all of these nations, gratuitous shootings not terrorist-inspired are extremely rare: about 4 in the UK in the last 40 years, though one was in a primary school (Dunblane). Norway suffered a terrible political-extremist massacre by one of its own citizens in Oslo in 2009; leaving over 70 dead.
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Whatever is wrong in the USA to make criminal shootings so casual and habitual, mystifies and saddens everyone else around the world - though might encourage those regimes that despise the American way of life - but it does seem based on deep social and cultural problems.
Those do include a widespread but by no means universal fetish for owning guns whose only possible purpose is killing people, including military-grade guns no civilian should ever "need". I don't claim that fetish as the reason for the gratuitous murders, just the means to commit them; but why own a gun anyway? What sort of gun?
If you buy a gun other than only the appropriate type solely for a genuine, controlled sports or farming purpose, are you prepared to shoot dead, fellow human beings? Just as some yob skulking around with a kitchen-knife is prepared to stab someone to death? Even in "self-defence"?
We foreigners must recognise that despite the estimated 120 guns per 100 adults, very many Americans do [i]not[/] own guns of any type. We must also recognise that the big-name, legal gun-clubs are proportionally very small in reality; but though they would presumably refuse membership to someone they suspect of criminal intent, some have large political-campaign funds for friends in high places, making any condemnation by them of gun violence rather hollow.
Nevertheless, does that gun fetish create a circle of fear leading to many others who would not otherwise dream of arming themselves, to do so?
That estimate includes a big jump in weapons purchases during the worst of the Covid pandemic - does anyone know why?
Only Americans can answer such questions of their "own" land; and to identify and overcome their own social and cultural problems, but one major obstacle seems a cultural tendency to reduce everything to mere money and shallow party-political bickering.
Does anyone in Wall Street and the Capitol look beyond bank balances?
All democracies disagree on party lines on how to run a country, but usually manage to work together, somehow. Is there no cross-Party co-operation in anything in the USA ?
A bullet can kill anyone, but it needs more than mere politics or a Constitution obviously open to being amended, to endeavour to ensure it is never fired in the first place.
It needs cross-floor political will, but also genuine, nation-wide shifts in society and culture.