Around 70 million people migrate between countries each year. This type of migration is less common than internal migration such as rural to urban migration. There are two reasons why international migration is less common. Firstly the longer distance involved and political controls make it difficult for migrants to move freely between countries.
The border between the USA and Mexico is more than an international frontier. It is a boundary where the rich are divided from the poor, Because of the economic contrast that exists on the other side of the border people are constantly attracted to the bright lights and big money that the USA holds.
At least 1 million Mexicans try to cross the border every year most of them illegally although the USA has an elaborate security controls along the border, it is impossible to stop everyone. Those illegal immigrants who are caught are deported back to Mexico. Increasingly Mexican immigrants are unwelcome in the USA as they are seen to drain the nations social security and welfare system.
In some places the scale of emigration is so high that population levels have fallen steeply. Santa Ines in NorthWest Mexico has lost two thirds of its population. But people leaving the village were not exactly poor. They left the country not out desperation but mainly to improve their quality of life. At one time only the men migrated and when they made enough money they would return home and share the wealth with their family. It is mainly young adults who migrate and so they leave ageing communities behind. With few children left, these communities will gradually die.
Immigrants have a deep impact on America. There is an ideal of America as a destination of hope and opportunity where the poor and the oppressed can make a new life but they bring with them a trail of tension between natives and newcomers, hostility expressed in job discrimination and riots, and laws designed to keep immigrants out rather than welcome them in. These newcomers were the people who built America. They dug canals, cut the timber and laid down the foundations for the megacity.
The greatest flow of immigrants took place between 1820-1920 when more than 30 million people poured into the USA. Around 8 million come from Mexico which created a mass overload on the country. One impact of the great diversity of people who have immigrated to the United States is frequent racial and cultural tensions. Clashes have forced America to confront the difficulties of accommodating such differences while remaining a democracy.