When people immigrate from one nation to another, the supply of labor in the destination nation increases. When the supply of something increases, the price decreases, so wages will fall. The immigrants will also spend money. Immigration increases the number of consumers, so consumer demand will increase, so consumer prices will increase. Businesses will have lower costs because wages are lower and higher revenues because consumer prices are higher.
Thus the short term consequences of immigration are lower wages, higher consumer prices, and increased business profits. People who own businesses become richer, while everyone else becomes poorer.
But what are the long term consequences of immigration?
The increased business profits will attract new businesses and existing businesses will expand. The new businesses and expanded old businesses will create new jobs and increase production of consumer goods. The demand for labor will increase, which will cause wages to increase. The new businesses will increase production of consumer goods. The increased production of consumer goods will cause the prices of consumer goods to decrease, especially when new businesses cut prices in order to gain market share. Businesses will have higher costs because wages are higher and lower revenues because consumer prices are lower.
Thus the long term consequences of immigration are higher wages, lower consumer prices, and decreased business profits. People who own businesses become poorer, while everyone else becomes richer.
The long term consequences of immigration are the exact opposite of the short term consequences of immigration. Thus the total consequences of immigration are nothing. Immigration does not make anyone richer or poorer.
Immigration makes business owners temporarily richer and everyone else temporarily poorer. How long does this effect last?
In an dynamic, unregulated free market economy, new businesses will appear and old businesses will expand very quickly. The effect of making business owners richer and everyone else poorer will not last long. The effect will disappear so quickly that the effect is almost nonexistant. The effect is probably too small to be measured.
In a static, heavily regulated economy, creating new businesses and expanding old businesses is difficult and slow. The effect of making business owners richer and everyone else poorer will last for a long time.
Immigration increases the number of people in a nation. More workers and more consumers means a larger economy. A larger economy will probably have more economies of scale and more specialization and division of labor. This makes the economy more efficient, which results in higher business profits, which results in more competition, which results in higher wages and lower consumer prices, which benefits most people. A larger economy will probably be more diversified, which makes the economy less vulnerable to economic problems.
However, a larger population also increases the demand for natural resources. A fixed amount of natural resources must by divided among more people. In rare situations, the disadvantages of a larger population might exceed the advantages of a larger population. But usually the advantages of a larger population exceed the disadvantages of a larger population.
Up to here, I have been assuming that immigrants were the same as natives, with the same skills and the same wealth. This simplifies the examples and makes it easier to understand the consequences of immigration. However, it is an unrealistic assumption. Why would anyone immigrate from one nation to another if both nations were exactly the same? In reality, immigrants are different from natives. Immigrants have different skills, different consumer preferences, and different wealth. Most immigrants move from a poor nation to a rich nation, and have fewer skills and less wealth than natives because poor nations have fewer opportunities for people to acquire skills and wealth. But some immigrants move from poor nations to rich nations because the immigrants are highly skilled, and there are more opportunities and higher pay for highly skilled workers in rich nations. And some people immigrate from rich nations to poor nations because the cost of living is less.
The largest benefits of immigrations occur because immigrants are different from natives. It does not matter what makes the immigrants different from the natives. Any difference between natives and immigrants benefits the natives.
Wealthy immigrants contribute capital to the economy, which benefits everyone.
Immigrants with special skills supply the natives with goods and services produced by the immigrants' special skills.
Immigrants without special skills take low wage jobs, which keeps business costs low, which keeps consumer prices low, which benefits everyone.
If the skills of immigrants are different from the skills of natives, then immigration will result in lower wages for the skills possessed by immigrants. This results in a higher standard of living for everyone else.
For example, most mexicans who immigrate to America 1990-2010 are unskilled and take manual labor jobs like harvesting fruits and vegetables. Since there are more workers seeking manual labor jobs, the wages for manual labor jobs fall. This results in a lower standard of living for natives with manual labor jobs. Business which employ manual laborers will have lower costs and higher profits, but higher profits will cause increased competition which will cause lower consumer prices and lower business profits. The lower consumer prices result in a higher standard of living for all natives who are not manual laborers.
There are fewer opportunities for americans to work as poorly paid manual laborers, but more opportunities for americans to work as well paid supervisors of manual laborers.
Computer programmers moving from India to America reduce the wages of computer programmers in America. This hurts american computer programmers. But this also reduces the costs of computer programs. This benefits anyone who buys computer programs, and anyone who buys anything from a business which buys computer programs.
Immigration hurts the small number of natives who are most like the immigrants, and helps everyone else. The number of natives who benefit from immigration is much larger than the number of natives who are hurt by immigration. The benefits of immigration are greater than the costs of immigration.
Immigrants benefit from immigration, usually because immigrants have higher incomes than in their former homes. The free market redistributes these benefits, so that both natives and immigrants share the benefits of immigration.
Opponents of immigration say that immigration causes unemployment amoung natives and reduces the standard of living of natives. This is not true. If immigration was restricted, there would be fewer workers, so wages would rise, so businesses would raise prices, so there would be inflation, so the monetary authorities would reduce the money supply, which would cause a recession, which would cause unemployment, which would cause wages to fall. The problems of unemployment and declining standard of living of natives would be worse without immigration. The unemployment and reduced standard of living of natives is not caused by immigration.
Proponents of immigration say that immigrants take jobs that natives will not do. This is not true. Natives would be happy to take manual labor jobs if only the employers would pay more. Immigrants reduce the wages in jobs preferred by immigrants, and the reduced wages cause natives to change to different jobs.
Opponents of immigration say that immigration should be restricted because immigration makes poor people poorer. But restricting immigration makes everyone else poorer. If it is bad to hurt one group of people, how can it be good to hurt a different group of people instead? A better way to help poor people would be to tax the large number of people who benefit from immigration and use the money to compensate the small number of people who are hurt by immigration.