The relative global decline of the United States has become a frequent topic of debate in recent years. Proponents of the post-American view point to the 2008 global financial crisis, the prolonged recession that followed, and China's steady rise. Most are international relations experts who, viewing geopolitics through the lens of economic competitiveness, imagine the global order as a seesaw, in which one player's rise necessarily implies another's fall.

But the exclusive focus on economic indicators has prevented consideration of the geopolitical implications of a US domestic trend that is also frequently discussed, but by a separate group of experts: America's ever-increasing rate of severe mental disease (which has been very high for a long time).

The claim that the spread of severe mental illness has reached "epidemic" proportions has been heard so often that, like any commonplace, it has lost its ability to shock. But the repercussions for international politics of the disabling conditions diagnosed as manic-depressive illnesses (including major unipolar depression) and schizophrenia could not be more serious.

It has proved to be impossible to distinguish, either biologically or symptomatically, between different varieties of these conditions, which thus constitute a continuum - most likely of complexity, rather than severity. Indeed, the most common of these illnesses, unipolar depression, is the least complex in terms of its symptoms, but also the most lethal: 20 percent of depressed patients are estimated to commit suicide.

Manic-depressive illness and schizophrenia both are psychotic conditions, characterized by the patient's loss of control over his/her actions and thoughts, a recurrent state in which he/she cannot be considered an agent with free will. Obsessive suicidal thinking and paralyzing lack of motivation allow depressed patients to be classified as psychotic as well.

These conditions are often accompanied by elaborate delusions - images of reality that confuse information generated in the mind with that provided from outside. Often the distinction between symbols and their referents is lost, and patients begin seeing people solely as representations of some imagined force. The judgment of such people cannot be trusted, to put it mildly.

A massive statistical study, conducted from 2001 to 2003 by the US National Institute of Mental Health, estimated the lifetime prevalence of major depression among American adults (ages 18-54) at more than 16 percent, and that of schizophrenia at 1.7 percent. There is no known cure for these chronic diseases; after onset (often before the age of 18), they are likely to last until the end of the patient's life.

Surveys among US college students estimated that 20 percent fitted the criteria for depression and anxiety in 2010 and nearly 25 percent in 2012. Other studies have consistently shown rising rates of prevalence with each successive generation, and it is argued that, if older statistics were faulty, they erred on the side of understanding the spread of mental illness.

All these suggest that as many as 20 percent of American adults may be severely mentally ill. In view of disputes over the significance of available data, let's assume that only 10 percent of American adults are severely mentally ill. As these conditions are presumed to be distributed uniformly within the population, they must afflict a significant percentage of policymakers, corporate executives, educators and military personnel of all ranks, recurrently rendering them psychotic, delusional and deprived of sound judgment.

If it is deemed sensationalist to characterize this situation as terrifying, one may add that a much larger percentage of the population (estimated at about 50 percent in the NIMH study) is affected by less severe forms of mental disease that only occasionally disturb their functionality.

Comparative epidemiologists have repeatedly noticed something remarkable about these illnesses: only Western countries (or, more precisely, societies with monotheistic traditions) - particularly prosperous Western countries - have prevalence rates of this magnitude. Southeast Asian countries appear to be especially immune to the bane of severe mental illness; in other regions, poverty, or lack of development, seems to offer a protective barrier.

As I argue in my recent book Mind, Modernity, Madness, the reason for the high concentration of severe mental illness in the developed West lies in the very nature of Western societies. The "virus" of depression and schizophrenia, including their milder forms, is cultural in origin: the embarrassment of choices that these societies offer in terms of self-definition and personal identity leaves many of their members disoriented and adrift.

The US offers the widest scope for personal self-definition; it also leads the world in judgment-impairing disease. Unless the growing prevalence of serious psychopathology is taken seriously and addressed effectively, it is likely to become the only indicator of American leadership. The rise of China is unrelated to this.

The author is a professor of Sociology, Political Scienc and Anthropology at Boston University, and distinguished adjunct professor at Lingnan University, Hong Kong.

Project Syndicate

(China Daily 08/02/2013 page9)