In the days after the deadly Paris attacks Friday in which terrorists coordinated shootings and bombings across the city, some American politicians -- including presidential candidate Florida Sen. Marco Rubio -- questioned whether the U.S. should be accepting refugees from Syria at all. The United States, however, has a vigorous refugee vetting process that can take years to complete and is much more extensive than the seemingly chaotic process often associated with European countries, according to human rights activists.

“No vetting process can make guarantees, but the population identified by the U.N. and vetted by both [the U.S. and the U.N.] has worked successfully in alleviating crises in dozens of other countries, including Iraq, the Democratic Republic of Congo, Somalia and the Central African Republic," Geoffrey Mock, the Syrian country specialist for Amnesty International USA, has said. "There’s no reason to believe Syria will be any different."

In order to receive refugee status in the United States, according to the State Department, individuals first need to be referred by official sources like the United Nations to the U.S. Refugee Admissions Program, which is run by U.S. Citizenship and Immigration Services. Applicants must meet specific referral criteria, including showing that they fear being persecuted or have been persecuted. The process is slow and almost always takes more than a year, though it can also take much longer.

That procedure is much more thorough than what is seen in Europe, where geography and proximity make it possible -- albeit still difficult -- for Syrian refugees to enter countries in the continent. Policies there generally allow asylum-seekers to enter a country without an extensive vetting process.

There have been 1,854 Syrians admitted into the United States since the Syrian civil war started in March of 2011. They have been sent all over the country. However, they tend to be concentrated in midsize cities where the cost of living is less than that of some larger metropolises in the country.

Several American governors have made moves to suspend Syrian refugee placement in their states. They include Michigan's Rick Snyder, Texas' Greg Abbott and Louisiana's Bobby Jindal, who, like Rubio, is a Republican candidate for president.