Overview6 copies each of all three reading levels, 18 books total. From the beginning of human history, people have moved from one place to another. They seek better jobs and schools and leave behind unstable political conditions and limited opportunities. These factors often cause people to immigrate from less developed countries to more developed countries. The same factors also lead people to migrate within a country. Migration examines the forces behind migration, the challenges that migrants face, and the ways in which new populations enrich their communities.