The causes of depression are not very well understood, but it is said that it may be do to genetic causes...in these ones the disease isn't triggered by any known psicossocial factor, last the entire life and it is the worst to deal with. Or it may be due to external causes.
Of course the two causes can act together.
I'm a "strange" person since I remember and almost everyone in my family had depression. Their depression was treatable and their fine now. So the genetic cause could be the one for me.
But in the other hand I have some traumas in my past and in my case the anxiety plays a bigger role than depression does. My education, my parents criticism, their demand for us to be the best, their emotional indiference, the fact they never gived us anything we want like an ice cream, or a doll (money wasn't a problem), being beaten everyday because things like a broken glass. And when they beaten us and we were crying they beaten us even more for us to stop crying.
I love my parents, they provide me anything I need, they really care about me, they're good people with good values and smart ones, but I think they had their issues too and we suffer because of that.
And you, do you find a cause for your disease?