I strongly believe that depression was always present, but was not evident until the term was coined, therefore being used in several mental diagnostics. I think this fits your information age idea. Of course the underlying causes range from life events to a much lower level cause such as changes to neurotransmitters pattern.

I think it is related to lack of the ability to control our environment.  I did some testing with the Learned Helpless model by Seligman and depression is far more commonly reported in women than men.  Seligman proposed that a part of that relates to women's inability to control their lives.  The increase in depression and there has been a significant increase in the US has been in men and I think it is extremely arguable that our social changes and even more importantly of late economic changes due to globalization and the loss of so many jobs due to outsourcing, economic stagnation in wages, difficulty in finding new employment that allows families to maintain their status in the middle class etc. all support a growing loss of control.  It is also beginning to be more socially acceptable for men to acknowledge their difficulty.

I would love to see some studies showing effects of various social and economic influences on the development of depression.  One other small factor may be that at least in the US psychological treatment was limited to a certain number of visits per year by insurance companies if it existed at all.  That has changed because of changes in the law and I was happy to see that all the insurance plans I have looked at recently have much more generous benefits which may improve the ability of individuals to access mental health care.

At present, depression is so common due to many factors & the main ones are: unemployment, financial difficulties, suffering from unjust persons & governments, sadness about personal & collective miserable conditions, and lack of sympathetic attitudes & behaviors in relationships.

What we call depression is a final common pathway and, if you consider only the symptoms, many conditions which look like depression are actually not depression.

For instance, patients with PTSD usually have depressive symptoms but their condition is different in the course, pathogenesis, and treatment response. You may check my work on dissociative depression (the few papers have been uploaded in Researchgate), a concept I have proposed to address the heterogeneity despite overlap in phenomenology.

Article Dissociative Depression Among Women in the Community

Dr. Nizar, that is a fine explanation for situationally induced depression, but there are many kinds of depression that are biologically and even evolutionary (passed familially) in nature.  No offense but your answer was a bit quick and simplistic.  I think an individuals response to your factors differ in huge measure by their perception of their own ability to influence the outcome of events PLUS a biologically induced predisposition to be able to deal with events.  Some people, myself for one, have a strong disposition to see things as temporary and controllable, others see things as permanent and uncontrollable.  Whether depression occurs may differ significantly on which of those groups you belong to and the extent to which you fall into that group.  It also relates to temperment things and issues like fight or flight response, which are definitely strongly influenced by biology

People will never be negatively emotional, if they are clear about the three questions: where are they from before life here? What's the meaning of living and life? Where will they go after death of the body?  To make sense of the three questions, one need to cultivate in a Buddhist way.  This answer is surely personal, something of my own experience. To know more, some books about reincarnation or previous life may help find a clue to the answer. 

Let's shift to Freud's and Maslow's theories, one word may be the key: imbalance. Some words more: the imbalance between the physical or mental needs and the dissatisfaction.

Zhang, that is a beautiful thought and I wish I believed that was the answer.  Certainly spiritual or religious views can offer protection against some mental illness, but it doesn't wipe out the effects of hormones, brain activity, brain receptors etc.  As an agnostic, my answers to your questions are probably counter to anything you believe.  Yet I also appreciate some Eastern practices as a means of dealing with life's stressors.  I read a book some years ago called "The Dragon Doesn't Live Here Anymore"  I loved it.  There were many suggestions that I incorporated in my life at a very difficult time which helped me to cope.  I lost that book and have been looking ever since for another copy.  But on the whole I am a scientist so don't believe in after life's, or coming from somewhere else pre life.  I wouldn't mind believing in reincarnation, except I want to remember my past lifes and the people in them so that I could learn from my mistakes.  Similarly I am bothered by death because of the separation from those I love.  If I could connect even on another plane I think I would rest more easily.  Otherwise it just makes me very sad to think of the day when I can't talk to my daughters or for that matter communicate my love to my doggies (I have three fabulous, wonderful, smart and loving Golden Retrievers that are family to my husband and I)  Anyway, that isn't what this question is about but your answer made me reflect a bit.  I am old enough now to be able to see the impending end of my life and so reflect on this end quite a bit some days.  (and I am healthy)

Dear Alexander,

         I am grateful for your response and reflections. 

        For me, Buddhist dharma is a set of cultiviating ways rather than a religion. In one of the Buddhist classics, Sakayamuni once and again taught his disciples not to be superstatious of his teachings because he was the Buddha, but to test them through practising and experiencing. 

       I have been doing one of the ways---the Buddhist chanting practice for three years and was fortunate and blissful to have attained and experienced part of Buddha Sakayamuni's dharma. By reading the preceding masters' works, I found our testifications were somewhat identical. Now I am not fearful or sad, or painful or regretful about any loss, even for the departure from my body. I will face it naturally and peacefully in the Buddhist chanting since mortaliy is nothing more than a change.  I enjoy a peaceful mind in most of a day. Though sometimes a little bit distracted or disturbed by the effect of hormones or brain activities,  in no time, I can notice it and come back to the state of tranquility. 

      The Buddhist chanting is one of the meditating ways that renders a passage to samadhi---a state of tranquility.

      Through meditation, the Buddha Sakayamuni attained the truth of the universe, that is change and emptiness.  Only through Buddhist meditation can the truth be attained and experienced. There are Three phases in the process. The first is satori---the state of spiritual enlightment---  comprehension of the true nature not only of yourself, but of the universe. Only then can one be freed, to most degree, from the material or spiritual shackles of desire and fantasies. Then comes the next stage, that is to culitivate oneslef, to struggle with and at length, to wipe out  the effect of hormones and brain activities. Finally attains the ultimate state of cultivation---Anuttara sammasambodhi---complete liberation from material and spiritual bonds and  permanent state of absolute tranquility.  

      I'm empathetic about your worry. But nobody can avoid the end of life. See it as a change---a farewell to our decaying body---into another form of being. Maybe the next life will turn up in a much purer, happier and fancier world. It's really worth expecting, ha？!

       As for me, the next world will be Nirvana. 

       p.s. The Tibetan Book of the Dead will do a lot of help understand the process of death and the next life. You can find the book at  amazon. com. or the video clips by searching [西藏度亡经]英文1-10 at baidu.com.