The second is agricultural societies. This kind of societies emerged after the invention of the plow. The plow brought about even larger supply of food, which allowed the development of cities. People now have more time to participate in other activities such as philosophy, art, literature, and architecture. This period is usually known as the "dawn of civilization" because the changes are so huge and profound. Social inequality raised. There were taxes, there were "subjects," and the elite surrounded themselves with armed men.
The third is the Industrial revolution which began in Great Britain. The steam machine was introduced to run machinery. This tool brought about even bigger social inequality, much more than any other ever seen. Those who first used this technology gathered immerse wealth, and the other peasants were kicked off their feudal lands and had to move to the city, where they faced hardships like starving, low wages, and stealing. This revolution brought about better conditions after the workers demanded for it. There were better housing, access to libraries and education, more variety of food, and the average person's life span was higher than any other period in humanity. Monarchies and dictatorships also moved to representative political systems. People received their rights to vote, and to rights to be tried and cross-examine witnesses. Women also gained greater rights than before.
And the fourth is the microchip, which allows the service industries to emerge. The United States have more than half it work force