Amount of peace and wealth are clearly not fully predictive of good mental health. Public health officials in England expected a civilian mental health crisis during WW2. This didn't happen, the incidence of "neurosis" remained flat.

On some level, humans thrive under hardship. Social cohesion goes up, meaning and purpose comes easy. People who lose their job become less happy, and do not recover until they get a job again. Bill Gates wakes up and goes to his job, not because he needs money but because he needs to matter.

This worries me about AI and automation, universal basic income is needed, but doesn't solve people's need for having a purpose.