Pew Research Center recently released a wonderful new report that estimates the illegal immigrant resident population in European Union and European Free Trade Association (EU-EFTA) countries. This is the first systematic report to estimate Europe’s illegal immigrant population along the lines that Pew and others use to estimate the U.S. illegal immigrant population. Illegal immigrants are a much larger population in the United States than in Europe.

Pew estimates that there are 3.9 million to 4.8 million illegal immigrants in EU-EFTA as of 2017. Those illegal immigrants come from countries outside of the EU-EFTA area. About 1 million illegal immigrants in EU-EFTA have pending asylum claims, so many will eventually earn legal status. As a percentage of the 525 million people living in the EU-EFTA, only about 0.74 to 0.91 percent are illegal immigrants. Of the roughly 20 million non-EU-EFTA residents who are non-citizens in any of those countries, only 19 to 24.5 percent are illegal immigrants.

Compared to the United States, illegal immigration is a minor concern in Europe. According to Pew, there are roughly 10.5 million illegal immigrants in the United States as of 2017. Other groups come to similar numbers despite some controversy regarding estimation methods. Illegal immigrants were roughly 3.2 percent of the approximately 326 million people living in the United States in 2017. Of the 22.6 million non-citizens currently living in the United States, about 47 percent are illegal immigrants. No matter how you look at it, EU-EFTA countries have a smaller illegal immigrant population than the United States.

There are many reasons why many fewer illegal immigrants live in the EU-EFTA than the United States. The first is geography. It’s more difficult for illegal immigrants to travel from poor countries to Europe illegally. Crossing the Mediterranean Sea is expensive, difficult, and deadly. Historically, crossing the border from Mexico into the United States was easier. That is why about 23 percent of the illegal immigrants in Europe are from other European countries outside of the EU-EFTA like Russia, Turkey, Ukraine, and Kosovo. The cost for them to travel to Europe is a lot lower than the cost for an Afghan, Iraqi, or Nigerian.

Another reason is that the EU allows workers from poorer countries to work in wealthier EU countries legally. A larger supply of legal immigrant workers crowds out illegal immigrant workers. For instance, Luxembourg was the wealthiest EU country in 2017 with a per capita GDP, PPP of $107,641 in current international dollars. Workers from Bulgaria, which is the poorest EU country, have a crudely-estimates place premium of 5.1 if working in Luxembourg. That’s much higher than the 3.1 place premium multiple (same crude estimation method) for Mexicans working in the United States. If the United States had a free movement agreement with a few countries as poor as Mexico then the illegal immigrant population here would also be a lot smaller too.

The third major reason Europe has fewer illegal immigrants than the United States is that they have had more amnesties in recent years. From 1996 to 2011, more than 5 million illegal immigrants were legalized in Europe. The last major U.S. amnesty was in 1986 for illegal immigrants who arrived before 1982 (DACA is merely a temporary reprieve with work authorization). By decreasing the stock of illegal immigrants substantially in recent years, EU-EFTA countries have kept the number of illegal immigrants low.

Some European countries have a revolving amnesty program that isn’t tied to the illegal immigrant’s date of entry. For instance, the United Kingdom has a revolving amnesty policy that grants “limited leave to remain” (i.e., temporary residence) to illegal immigrants under certain conditions that can lead to “indefinite leave to remain” (i.e., permanent residence). The United Kingdom grants limited leave to remain to any adult non-UK citizen who would have “very significant obstacles” to “integration into the country to which he would have to go,” children who have lived continuously for at least seven years in the United Kingdom and for whom it would not be “reasonable” to expect them to leave, non-UK citizens ages 18–25 if they have lived continuously for at least half their life in the country, and any non-UK citizen who has lived continuously for at least 20 years in the country. Limited leave to remain provides for two and a half years of temporary residence without access to public benefits, but immigrants may renew it. Following 10 years with limited leave to remain, legalized immigrants may apply for indefinite leave remain.

Another reason why there are fewer illegal immigrants in Europe is that the generally more intrusive labor market regulations and identity systems in EU_EFTA countries make it more difficult to work, rent a dwelling, open a bank account, or otherwise live in Europe as an illegal immigrant than the comparatively less-regulated United States. A Danish libertarian told me that the Personal Identity Number issued to legal immigrants and Danish citizens is essential to get a job, receive payment, rent an apartment, and open a bank account. There’s likely a black market for Personal Identity Numbers, some fraud on the margins, and other ways to circumvent the system, but only at a cost. Meanwhile, American attempts to create similar systems fail miserably.

Costly labor market regulations that discourage the hiring of low-skilled workers means that employers of illegal immigrants in Europe would have to break both labor market laws and immigration laws. In the United States, by comparison, employers only break the comparatively less-well enforced immigration laws to employ illegal immigrants. This is why many American intellectuals who want harsher immigration enforcement push for a higher minimum wage – it will price out some illegal immigrants and conscript labor bureaucrats into immigration enforcement. The comparatively less-regulated United Kingdom, Germany (after the Hartz Reforms), and Italy’s large labor black market help explain why most illegal immigrants are in those countries.

The United States has one big lesson to learn from Europe’s experience with illegal immigration: A free movement zone with comparatively poorer countries can reduce illegal immigration. An increased supply of legal immigrant workers can crowd out illegal immigrant workers.