@Forever Sleep hit the nail on the head.
Depression is a "disease of civilization" in the sense that our advances have kind of been a tradeoff between our most base needs and our higher needs: for example, most people in WEIRD (western, educated, industrialized, rich, democratic) countries now have dependable access to food, water, and shelter, but don't have a small, tribal group that they feel a deep sense of responsibility and belonging to (which is what we're evolved for).
The challenge for future generations is going to be playing catch-up and finding a way to have both. We're pretty new at this whole technological civilization thing so we still have time to figure that out, but it will be at the cost of the generations (like ourselves) that got caught in the middle, in the transition period (assuming we ever do successfully make the transition, which judging by our current trajectory, is looking dicey).