It isn't just in the USA where people have run amok (see medical definition of amok from Merriam-Webster). The NEJM article says that such US tragedies are "entirely preventable" by the implementation of policies requiring that firearm sales involve background checks on purchasers and also allowing courts to have firearms removed temporarily from people who pose an imminent hazard to others or themselves but are not members of a prohibited class. These policies may well reduce such incidents, but the article doesn't provide any evidence to suggest that their implementation will prevent mass shootings entirely. And there must be questions about whether they really go far enough.
Amok episodes normally end with the attacker being killed or committing suicide. Murders which are followed by suicide are most likely to be committed in anger by aggrieved people blaming others as well as themselves. Although amok was traditionally seen as a syndrome bound to cultures such as Malaysia and Indonesia, all societies, including American society, can subtly sanction such mass shootings (and perhaps also not so subtly sanction them - eg. How does NEJM publish an article like this that doesn’t properly consider removing guns from civilian possession). The American government and people need to understand the ways in which they themselves are doing this. Amok isn't just happening in other parts of the world.