Migration is the part of life for birds and animals for millions of years. For the different season, to be in the different places, away from harsh nature is to comforts from any severeness. Still happening in greater number everywhere except humans who thought enough is enough, let's stay and face the challenges. Wow, that's awesome, the civilization was born. So those who stayed in the different places, formed different race, different culture and language with borders around. All kinds of people (religious) have to live together, if something goes wrong between them, the weaker must retreat...