The past century has seen a massive contrast of setting and ideas. Music has made a wide spread wave of culture, as well as movies and inner-cultural norms. People are now being effected heavily by a cultural shift, changing the inner-workings of old time society. Entering this subject, it is obvious that the happiness of men and woman of the world is effected by a massive amount of influences.
A large cultural shift that is hitting places in America especially, is the decrease of Christianity as a standard. This comment is simply commenting on the spiritual changes of the population. The effect of this notion would lead to instability in beliefs, as well as morality no longer being a standard. In a larger overview, this simply means that some people, because of a lack of a religious belief, perhaps have less of a theoretical grasp on life and its consequences, thus making them less happy because of confusion. Also, many people because of a lack of a belief in an eternal consequence are more prone to participating in behaviors not healthy for them, whether it be abnormally high rates of unsafe sex, or the use of drugs. The effects later in life, as proven by many studies that can be found easily without a citation here, would cause unhappiness, as it creates more instability and confusion. The ones who are happy are mainly the ones with a set vision of life, and its aftermath, thus making life easier to go through. Perhaps also the happiness levels of individuals would also come from influences from media, such as movies and music.
With the arrival of television, radio, and portable media everywhere in the world, every cultural influence imaginable could be transmitted to anywhere in the world. Those who take the cultural influences they receive as truth could be either happy or unhappy, depending on their status and beliefs. Therefore, its also simply the opinions of those who receive the cultural messages that effect the happiness of the masses.
In conclusion, the cliche answers are usually the best, beliefs that relate to spiritual experimentation as well as beliefs that effect people's thoughts about themselves from the media, are usually the culprits that effect the happiness of the masses, and act as mediums to effect the higher happiness in some that others do not have.