The USA government was shaken by a mass shooting case happened in Dec. 14 in Connecticut.
Reuters: Connecticut gun rampage: 28 dead, including 20 schoolchildren
According to the reports, the offender killed his mother and went to an elementary school, to shoot children. Twenty-six persons including 20 children were sacrificed. It is the most tragic massacre case in the USA.
The USA society is relatively tolerant for citizens to have a gun. Now the Brady gun control law requires licensed gun dealers to examine buyers not to sell guns to drug abusers or mentally ill persons. But this legislation hardly prevents gun crimes, I think. Severely mentally ill person cannot buy a gun whether the legal restriction exists or not. On the other hand, a person with deep menace can easily disguise his status.
In the USA there are debates whether gun control should be strengthened or not.
The New York Times: Debate on Gun Control Is Revived, Amid a Trend Toward Fewer Restrictions
Of course gun sellers will oppose to strengthen the restriction. Some libertarians are likely to claim that they have a right to protect themselves with their own.
In Japan, possession of arms is strictly restricted traditionally. I have not ever seen a real gun or even Samurai sword. Japan has strengthened the regulation more strict about possession of knives since 2007. I remember that was enforced after a criminal case with a knife.
How is the difference between two countries?
It is logically explained with Nash equilibrium.
The Nash equilibrium is invented by Jon F Nash, a mathematician. It means that each player of the game has no alternative to improve their interests. In a situation of Nash equilibrium, we hardly make any changes.
Wikipedia: Nash equilibrium
In Japan, there was no gun in modern society. If someone wants to possess a gun, he will be blamed heavily by other people. So it is reasonable that we all continue to adhere the regulation of gun control law.
In the USA, guns are used historically. If everyone wants to eliminate guns, the first person drops his gun must take a risk to be shot. Since outlaw is the last person to drop a gun, innocent people tend to get severe disadvantage. After all, nobody can drop guns.
The situation may be not so simple. Nonetheless it is possible that historical background that was occurred by chance makes the current issue complicated. And this is one of the reasons why we hardly import the idea born in foreign country easily.