Here are some facts courtesy of the Migration Policy Institute.
“* Until the late 1980s, more people were leaving Spain than coming in. Similar to Portugal and Ireland, Spain was a country of emigration. The tides changed and from 1990 on, Spain increasingly became a transit country for African migrants headed north, a receiving country for foreign laborers, primarily from Northern Africa and South America, and a place to retire for well-off Europeans.
* Today, Spain is Europe’s leading country of immigration adding more than 4.6 million immigrants (i.e., foreigners or persons without Spanish citizenship) between 1998 and 2008. The size of the foreign population in 2008 was 5.3 million out of a total population of 46 million. In 2008, Spain’s foreign population was higher than that of the United Kingdom (4.2 million).
* Foreigners’ share of the total Spanish population rose sevenfold from 1.6 percent in 1998 to 11.4 percent in 2008.
* Moroccans accounted for the largest share of the foreigners in Spain from 1998 through 2007, but were surpassed by Romanians in 2008 who accounted for 13.9 percent (or 731,000). Other large immigrant communities in Spain in 2008 were Moroccans (653,000 or 12.4 percent) and Ecuadoreans (428,000 or 8.1 percent). The top three countries of origin accounted for 1.8 million people, or more than a third of the foreign population in Spain in 2008. Since the late 1990s, Spain has absorbed a large and extraordinarily diverse immigrant flow from three continents: Europe, Africa, and South America.
* In 2008, the number of new arrivals fell 25 percent to 692,000, down from 920,000 in 2007. The greatest decline came from other European countries. For example, the flows from Romania and Bulgaria fell by more than 60 percent. There were slight declines in the number of migrants who came from Africa and Oceania in 2008; flows from the Americas declined by a quarter and those from Asia by 10 percent.
* The number of foreigners who acquired Spanish citizenship increased every year between 1997 and 2007 (except between 1999 and 2000). More than 71,000 foreigners became Spanish citizens in 2007.
* More than 7,600 new applications for asylum were made in 2007, 44.6 percent higher than in 2006 (5,297), but substantially lower than in 1993 when about 12,600 asylum applications — the highest in nearly three decades — were submitted.”
Allowing immigrants to become full citizens is a key policy for long term economic stability. Countries that do so attract migrants looking to become long term productive residents. This could be an important factor helping to mitigate demographic pressure on social support systems for countries like Spain with aging populations.
Also, I think it is likely that foreign born citizens are likely to have greater interest in maintaining the stability of the national government in their new country, due to their tending to not having ties to vested interests in historical separatist movements.