“Social trust” is, well, what it sounds like: How much do you trust your neighbors? And in turn, how trustworthy are they? In a low-trust place such as Greece, people don’t trust their neighbors not to cheat, which in turn makes them more likely to cheat themselves, because why should you stay honest when everyone else is getting away with something? This affects everything: whether people pay their taxes, whether they take benefits they don’t really need, how easy it is to regulate companies. And social trust also works as a productivity booster, because you can do away with a lot of the cumbersome monitoring that is ubiquitous in modern societies — the supervisors who oversee low-level workers, the store clerks who keep an eye on the customers. Every worker who is not making sure that people don’t steal or shirk can be re-employed doing something that actually increases output.

The United States simply doesn’t have that level of trust. And while it would be nice to think that we could get there if companies and government simply stopped acting so suspicious, the fact is that they frequently act suspicious because, well, Americans cheat more than Danes do. (Compare, for example, the American and Danish rates of tax evasion). Moreover, the mutual suspicion that Americans feel for each other restricts the range of politically feasible policies.

How the erosion of trust leads to murders and mass shootings

But while we all know from experience that shootings can lead to faltering trust, the reverse appears to be true as well. My research has found that declining trust in our institutions, our social structures and one another leads to more lethal violence, including mass murder. As abstract as these sentiments may seem, they predispose certain people to kill. In fact, they explain homicide rates better than any other factor, including unemployment, guns, drugs or a permissive justice system.

When we lose faith in our government and political leaders, when we lack a sense of kinship with others, when we feel we just can’t get a fair shake, it affects the confidence with which we go about our lives. Small disagreements, indignities and disappointments that we might otherwise brush off may enrage us — generating hostile, defensive and predatory emotions — and in some cases give way to violence.