Many immigrants from European countries and ethnic groups came to the United States during the 19th century and early 20th century, until the Immigration Act of 1924 was passed.
However, it seems as if few immigrants came from these countries: France, Portugal, and Spain. I wonder why.
If you could tell me, and also have links and citations for the reasons why they didn't immigrate, please list them below.
By French, I mean people who immigrated directly from France, and not French Canadians. By Portugal and Spain, I mean people who immigrated directly from those countries, and not from countries in Central and South America.
Thank you, in advance, for your information; I appreciate it.
EDIT: Your answers have been very illuminating. Thank you all for posting them -- even the ones that have been removed.
One simple explanation is just that those countries, Spain, France and Portugal all had significant empires in the New World and Africa- colonies filled with people who already spoke their language and where being a citizen of the mother country brought huge advantages. There was plenty of emigration from those countries, just not to the United States.
As far as France is concerned, it was mainly because of its demography. Basically, European countries went through demographic transition during the 19th century. That is to say, from high fertility and high death, to low fertility and low death rate as of today. Normally, the death rate decreases many years before the fertility rate, creating a demographic explosion. The UK, Italy, and Germany's population exploded in the 19th century, and they just couldn't sustain it so many of these people emmigrated to the US.
However, France demographics was unique: the death rate and fertility lowered at the same time, and thus France did not experience a demographic boom. http://en.wikipedia.org/wiki/Demographics_of_France
Note that French Canada did have a demographic boom and that most Americans with "french roots" are in fact from French Canada.
France became an immigration country, like the US, while its European neighbours were emigration countries. So very few people did emigrate to the US because there was no need.
On top of that, culturally speaking France has never had a population colony (even Algeria was largely populated by Spaniards and Italians). Even before the demographic transition, few people emigrated from France. It shows when you see the population of the British colonies and French colonies in America at the beginning of the French and Indian War. There were 75,000 French colonists in America by the mid 18th and 1.5 million Brits. French people just don't emigrate.
AS for Spaniards and Portuguese, as someone else said, they mainly emigrated to South America, and then to France!