Migration is a huge deal in the world today. It is almost a bigger deal now than it was in the past. Not because more people are migrating, actually less are, but now it has more of an effect on the world than it did before.
Push/pull factors are probably the main reason why people migrate. The Irish moving from Ireland during the Potato Famine, Mexicans crossing the border to America for better paying jobs, and even Americans moving to other countries. Whatever the push/pull factor there is always somebody who is not happy with where they are living and/or want something better that they believe they can find by simply moving to another country.
I used the example of the Irish fleeing Ireland because of the famine because this is a great example of how economies and communities can be altered as a result of migration. Many thousands of Irish left Ireland and a large deal of them wound up in cities like New York and Boston. This altered the economies of these cities because the Irish were willing to work for almost no pay. With this many more people elections were changed. Politicians now had thousands more votes to buy. Many of the Irish men also joined the union to fight in the Civil War adding additional troops that otherwise would have been there.
The other lesser common cause of migration is forced migration. When people are forced out of their homeland. Examples of this are The Lost Boys from Sudan and even the Cherokee on The Trail of Tears. Forced migration tends to be much different in the fact that those people don't want to give up their culture. With voluntary migration we see a melting pot effect where people conform to new local culture but hold on to some of their own. With forced migration people want to keep doing things the way they have always done them. They want to make their new home the same as their old home.
