What role should be played to make our country happy and prosperous? Well, it all comes down to the country in question and the resources and infrastructure in place... But I would say the number one way countries can improve themselves, become prosperous, and generally improve quality of life and the happiness of their population is to invest in education.
A more educated population will result in more innovation and industry, and this should improve the wealth of the country as a whole, and the aspirations and progress of the nation for the future.
Don't underestimate things though. Making a country happy and prosperous doesn't happen overnight, it is not easy and it is not always pretty. Sometimes hardship, violence and even ruthlessness have a part to play.
Look at all the major world powers in the world today: Every single one of them once had an empire, usurped other countries, and exploited people to get where they are!
