My citizens are unhappy. What should I do?
Pay attention to the morale of your people – if they are happy and satisfied, they will serve you better! A disgruntled population is significantly less productive and even refuses to go to war for you or trade. So take care that your people always happy or even delighted. You can achieve this by building decorations and cultural buildings. Advanced roads also provide for happy citizens and some Great Buildings like the Hagia Sophia, Frauenkirche of Dresden or the Alcatraz.
You will get your people enthusiastic when you will reach 40% of your population as extra happiness. This will give you a +20% towards your coins and supplies production.
To tell how much happiness you need based on your population, simply multiply your current population by 1.4.
Unhappy population - productivity is at 50%
Happy population - productivity is at 100%
Enthusiastic population - productivity is at 120%