In the United States, more than a dozen people have been arrested in the past year for trying to join the Islamic State, the militant group in Iraq and Syria. Above, an ISIS fighter holds the group's flag and a weapon in Mosul, Iraq, June 23, 2014. Reuters/Stringer

Three Brooklyn men originally from Uzbekistan were arrested Wednesday on charges of trying to join the Islamic State group. Their arrests are the most recent in a spate of cases this year and in 2014 where Americans, or immigrants living in the United States, have been arrested for trying to join or aid ISIS. In 2014, at least 15 U.S. citizens were detained for trying to join the terror group. Most were young and Muslim.

On Feb. 18, an Iraqi who held a U.S. green card was arrested in Detroit, accused of attempting to travel to Iraq and join ISIS. Al-Hamzah Mohammad Jawad, 29, was arrested at the Detroit Metropolitan Airport as he was boarding a plane to Amman, Jordan. On Feb. 8, six Bosnians were arrested in the U.S. and charged with providing and conspiring to provide material support to terrorist groups. Three were naturalized U.S. citizens.

In January, Christopher Lee Cornell, a 20-year-old convert to Islam from Ohio, pleaded not guilty to charges including attempting to kill government employees and possession of a firearm. Cornell, who U.S. officials said was plotting an attack on the U.S. Capitol, initially caught the FBI’s eye after writing on social media about supporting violent jihad. A criminal complaint stated that Cornell had written, “I believe we should meet up and make our own group in alliance with the Islamic State here and plan operations ourselves.”

In December 2014, three teenage siblings from Chicago were detained at O’Hare airport before they could fly to Istanbul and from there drive to Syria and join ISIS. They were Muslims of Indian descent, and the eldest sibling, Mohammed Hamzah Khan, 19, was charged with providing material support to a terrorist organization, charges to which he pleaded not guilty. If convicted, he could spend 15 years in prison. His siblings, who were minors at the time of arrest, have not been charged. Khan’s mother has said her son was recruited through social media by the Islamic State, which uses online networks including Twitter and Facebook to attract and recruit fighters.

Two months before Khan was caught, in October 2014, three teenage girls, one of Sudanese descent and two sisters of Somali descent, tried to fly to Turkey from Denver but were caught in Frankfurt by German authorities and returned to the United States. U.S. officials have said the girls had planned to join ISIS. They were 15, 16 and 17 years old.

In September 2014, Mufid Elfgeeh, 30, of Rochester, New York, was arrested and charged with three counts of attempting to provide material support to a foreign terrorist organization, among other charges, by trying to recruit people to join ISIS. He was arrested after trying to buy handguns with silencers from an undercover FBI informant, whom he tried to recruit to go to Syria and fight for ISIS, according to NBC News.

Shannon Maureen Conley, a 19-year-old convert to Islam from Colorado, was arrested at Denver International Airport in April 2014. She was on her way to Turkey by way of Germany so she could marry a member of ISIS she had met through the Internet. She pleaded guilty to the charge of conspiring to provide material support to a designated foreign terrorist organization and in January was sentenced to four years in prison, CNN reported.

These arrests at home are the more visible side of Americans who support ISIS -- a group limited to those who were caught before physically joining the organization. As for those who may have trained with ISIS or other terrorist groups outside of the U.S. and have subsequently returned to living in the United States, “it’s not even close to being under control,” FBI Deputy Assistant Director Michael Steinbach told the House Homeland Security Committee on Feb. 11. "It would not be true if I told you that we knew about all of the returnees.”

Americans are not the only ones inspired to join ISIS. From Britain, five people every week are joining ISIS, or more than 500 in total as of October 2014, while 90 Australians have been estimated to be fighting with militant groups in Iraq and Syria. From Belgium, 250 to 400 fighters had joined ISIS as of September 2014.