The “centroid” refers to the geographic center of the population of a country. So, if more people in a country live in the West than in the East, the “centroid” will be further west. The “centroid” of the United States has moved consistently west and south basically since the country was founded. This is because a larger and larger share of the population is living in the West and the South. This is primarily a consequence of migration from the East to the West and from the North to the South.

The “Sun Belt” is the name used to describe much of the South and West of the United States. Beginning in the second half of the twentieth century, cities in these regions experienced dramatic population growth as many Americans migrated away from the Northeast and the Midwest. Chicago is a northern city, so it is not considered part of the “Sun Belt.”

The “Great Migration” began in the late nineteenth century and continued throughout much of the early twentieth century. It involved the migration of African-Americans from the Deep South to cities like Chicago, Baltimore, Philadelphia, and New York - the industrial centers of the American northeast and midwest.

A Push factor is a reason to leave a country while a pull factor is a reason to move to a country. If the country which someone is living in is at war, they are pushed to leave for fear of their life and livelihood, especially if their lives were particularly endangered. 

While moving to a country that has more job opportunities is what often happens, this is a pull factor to pull someone to a country rather than a push factor which pushes someone out of a country.  

Often the country that they are leaving is their native country and the country they are migrating to is foreign to them.  If they are not living in their native country, that is not a push factor to leave although it could be a pull factor to return to their homeland. 

Natural disasters are surprisingly not often considered in the process of migration. Even if they were taken into account, people would not purposefully migrate to a region that has more natural disasters than the region they are already in. 

Someone who is forced to leave their home country is a refugee, regardless of what country to which they migrate. 

An illegal immigrant is someone who illegally immigrates into a country that is not their home. If they illegally immigrated due to being forced to leave their country under persecution they claim refugee status and are classified as a refugee and not as an illegal immigrant. 

There were many Soviet refugees during the break up of the U.S.S.R. and there still are many refugees who are Soviets. But the definition of a Soviet does not equal someone who is forced to migrate due to persecution. The definition of a Soviet is simply someone from the Soviet region of Eastern Europe and Western Asia. 

A prisoner of war is not forced to leave their home country due to persecution. Rather, they are persecuted in a foreign country due to the war that is on-going. They are under captivity in a foreign country.