There are many cultures who are nomadic. There are three different kinds of nomads.
The first group are hunter-gatherers. They move from land to land hunting and gathering foods. When the land is used up, they move on to a different piece of land. They also move according to the weather. This is the oldest kind of nomadic activity.
The second group are peripatetic nomads. These nomads possess a certain specialized skill. They are very important because they can offer the settled people a service.
The third group are pastoral nomads. These nomads use the land to graze livestock. They also move from land to land.
Settled people do not like nomads because they invade their land. Sometimes the nomads are respectful but many times they will stay on the land and use it, letting their livestock graze leaving nothing behind. This can be detrimental to the settled peoples survival.
Nomads and settled people tend to dislike each other because Nomads use up the land as they move from place to place. They allow their animals to graze until there is nothing left to graze on. Nomads have sometimes been known to steal from the farmers crops to feed themselves. If a farmer has a pack of animals he is raising and there is no more grazing materials for the animals to eat, he has a problem. There has always been competition for land and resources between farmers and hunters and gatherers.
I'm sure you'll receive answers from editors with social science backgrounds that will relate directly to your question. That is not my area, but I can give you a fundamental answer concerning how the human brain works.
Humans are by definition egocentric. Reality is known to us only by what our senses feed to our brains. Everything we experience, of course, is experienced from our own, extremely limited point of view.
Therefore, anything different from our own perspective is foreign.
Our brains are also wired to quickly categorize and label new information, and then file it away, much like what we have our computers do when we place information into files.
When we are exposed to something new, then, it is naturally foreign, or alien to us. Yet, we still categorize and label the information, we can't help it. Once these first impressions are filed away, they are difficult to rewrite. And unfortunately, human first impressions are almost always wrong. Our brains attempt to do the impossible: people are too complex to be summed up and categorized by a first impression.
Thus, nomads would tend to be suspicious of settled peoples, and vice-versa. Only experience and education can improve our reactions to others.
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