Civilization is basically a vital kind of grouping. Without civilizations, the world as we know it would not be. Civilizations have different qualities than regular groups of people such as nomads. For example, a civilization develops surpluses of things which helps the people be a stable community. These surpluses also create the construction and growth of cities and helps develop secure, formal states. Government is also present in civilizations. One very important part of a civilization is an advanced writing method. A civilization can only be complete with all of these factors, or it will just fall apart.
Nomads are nowhere close to being a civilization even though sometimes groups of nomads have good technology. Nomads travel around all the time following food. A civilization is a stationary place with agriculture. This means that the community of people occupying this civilization does not have to go running around scrounging for food. Nomads are just a small group of people without cities, sometimes without writing, no organizations, and their technology is lacking. Civilizations have the one-up on nomads without a doubt. If everyone was just a bunch of nomads, the world would not be organized, and cultures would not be as complex and great as they are today. Nomads are just a bunch of underdeveloped, not modern, and sometimes barbaric people.
The Greeks and the Romans both thought of themselves as a civilization separate from everyone else. The Greeks believed that anyone who could not speak Greek were barbarians meaning "those who cannot speak Greek." Anyone that could not speak Greek were only speaking "gibberish" to the Greeks so they separated themselves from others making themselves their own civilization.