I would actually venture to say that it is the lack of social support, social cohesion, and community that might lead to a MLC among Americans, not an excess of wealth.* **
It could be. But Americans aren's the only ones having a MLC. Several here are (or their MLCers are) from Canada Europe, Australia or New Zealand, to name a few,
When it comes to some European cities there also isn't much of a sense of community and as for social cohesion, Europe is super devided at the moment - we're lucky if another war does't break out soon. Not sure if you guys know how on fire things are at the moment in Europe -, and has been for several years, and, in cases, decades.
I don't know about social support. If you are talking state one, EU countries, at least some of them, have a good one. Neighbourhood level one has been eroding more and more.
Maybe the problem is not so much wealth of any sort in itself, but never being satisfied? That seems to be the case with MLCers.
* Caveat that I think there is still some type of biological cause/susceptibility at play.
So do I. But become super stressed and depressed because one thinks what one has is not enough, or because one is been over working to have tons of irrelevant things, ends up being a neurologic cause since burnout comes from excessive stress and depression is neurologic.
MLC, like other things/illnesses could have several causes. For example, pneumonia may be caused by viruses, bacteria, or fungi or, to a lesser degree, by other factors.
Sometimes good things fall apart so better things can fall together. (Marilyn Monroe)