In 1851, a white medical doctor in Louisiana (Dr. Samuel Cartwright) published an article in a medical journal in New Orleans discussing a new form of mental illness called "Drapetomania" -- this mental illness only affected enslaved African-Americans, and its chief symptom was that it made them attempt to run away from plantations. In other words, a real medical journal published an article which claimed that the Underground Railroad was a form of mental illness. Now it is important to note (in fairness to the medical profession) that most doctors did not agree with Dr. Cartwright's racist suggestion -- in fact, he was generally mocked for publishing the article.
This story is important today for showing the way in which the general power dynamics of society can be reflected within the medical profession. We know today that slavery is evil, and that women are allowed to vote -- nobody in 2014 thinks that a slave who flees from a plantation or a woman who suggests that women should have the right to vote is suffering from mental illness. But it is important to understand the history of these issues to show that the assumptions made by therapists can frequently reflect the power dynamics of society in the worst ways.
We should also note that, just as our ideas of justice can change over time with history, so too can the definition of psychological problems change over time. To return to the starting example of "hysteria" -- the mysterious female psychological condition which Sigmund Freud began his career by investigating -- we should observe that the actual symptoms that Freud was examining do not exist anymore. Female hysterics of the late nineteenth century were placed under medical care because they had the sudden paralysis of an arm or a leg, and had not suffered a stroke or any other physiological cause that would explain the paralysis. Instead the paralysis was understood to be psychological in origin. In 2014, we would have to look for a long time to find anyone with symptoms like this, even though the symptoms were common enough 125 years ago that psychiatrists could examine multiple patients displaying different versions of these symptoms. So where did this disease go? The simple fact is that symptoms may in fact be a reflection of the society in which patients find themselves. The crucial thing is to know that therapist and patient are both part of historical processes they did not cause.