The United States has the largest number of civilian guns in the world, with about 120 guns per 100 people, or more guns than the population. In the United States, people can be victims of gun violence, whether in grocery stores, shopping malls, or in schools. The United States is the only developed country in the world with frequent gun violence cases, which is a unique American phenomenon. In recent years, the gap between the rich and the poor in the American society continues to widen, and problems such as corporate layoffs, business closures and economic downturn have led to further social fragmentation, and some groups sliding to the edge go to the extreme due to psychological loss. The proliferation of gun violence is destroying the social trust in the United States, distorting the collective psychology, and boosting the proliferation of shooting violence, making more people want to protect themselves. By far, "self-defense" has become the most important reason for gun ownership among Americans today, more than hunting, entertainment, collecting, work, etc.