Why attackers keep targeting Europe

Before you go, we thought you'd like these...

Europe's Recent History of Homegrown Attacks

The terrorist attacks on Brussels' airport and metro system that killed at least 31 people on Tuesday are the latest in a wave of large-scale attacks against European countries over the past 15 months.

Paris was hit twice last year. Then Turkey, which wants to join the EU, suffered several deadly bombings, the most recent of which happened just over a week ago. And then came the Brussels attacks.

As was the case with many of the others, the Brussels bombings were targeted, well-coordinated and designed to inflict maximum damage by striking packed public areas.

An offshoot of Al Qaeda took responsibility for the first Paris attack in January 2015, which targeted the Charlie Hebdo newspaper and a kosher market. The Islamic State (ISIS) has claimed responsibility for the second Paris attack, some of the bombings in Turkey and Tuesday's attacks in Brussels.

SEE ALSO: Live updates: At least 31 dead in Brussels terror attacks

There has been one major ISIS-linked attack in the United States, in San Bernardino, California, last December. But that was perpetrated by two ISIS supporters, not skilled militants trained by the group.

The U.S. has been thought to be the highest-profile target for ISIS and is the most frequent target of its threats.

Memorials made after the attacks:

58 PHOTOS
Memorials in Brussels after attacks
See Gallery
Why attackers keep targeting Europe
People holding a banner reading "I am Brussels" behind flowers and candles to mourn for the victims at Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)
Young women hold each other at a makeshift memorial in front of the stock exchange at the Place de la Bourse (Beursplein) in Brussels on March 22, 2016, following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. A series of explosions claimed by the Islamic State group ripped through Brussels airport and a metro train on March 22, killing around 35 people in the latest attacks to bring bloody carnage to the heart of Europe. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
People bring flowers and candles to mourn at the Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)
BRUSSELS, BELGIUM - MARCH 22: People gather at Place de la Bourse in support of the victims after the terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Aurelien Meunier/Getty Images)
TOPSHOT - A photo taken on March 22, 2016 shows a sign peace made of candles in front of the Bourse of Brussels in tribute to the victims of Brussels following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. Belgium launched a huge manhunt on March 22 after a series of bombings claimed by the Islamic State group ripped through Brussels airport and a metro train, killing around 35 people in the latest attack to bring carnage to the heart of Europe. / AFP / BELGA / Aurore Belot / Belgium OUT (Photo credit should read AURORE BELOT/AFP/Getty Images)
TOPSHOT - People light candles in tribute to victims at a makeshift memorial in front of the stock exchange at the Place de la Bourse (Beursplein) in Brussels on March 22, 2016, following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. A series of explosions claimed by the Islamic State group ripped through Brussels airport and a metro train on March 22, killing around 35 people in the latest attacks to bring bloody carnage to the heart of Europe. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: A young girl lights a candle at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)
TOPSHOT - People stand hand in hand in tribute to victims at a makeshift memorial in front of the stock exchange at the Place de la Bourse (Beursplein) in Brussels on March 22, 2016, following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. A series of explosions claimed by the Islamic State group ripped through Brussels airport and a metro train on March 22, killing around 35 people in the latest attacks to bring bloody carnage to the heart of Europe. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People gather to leave tributes at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)
A message written on the ground reads 'Brussels is beautiful' next to flowers and candles following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People gather at Place de la Bourse in support of the victims after the terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Aurelien Meunier/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People gather at Place de la Bourse in support of the victims after the terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Aurelien Meunier/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People gather at Place de la Bourse in support of the victims after the terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Aurelien Meunier/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People gather at Place de la Bourse in support of the victims after the terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Aurelien Meunier/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People gather at Place de la Bourse in support of the victims after the terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Aurelien Meunier/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People gather at Place de la Bourse in support of the victims after the terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Aurelien Meunier/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People gather at Place de la Bourse in support of the victims after the terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Aurelien Meunier/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People gather at Place de la Bourse in support of the victims after the terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Aurelien Meunier/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People gather at Place de la Bourse in support of the victims after the terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Aurelien Meunier/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People gather at Place de la Bourse in support of the victims after the terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Aurelien Meunier/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People gather at Place de la Bourse in support of the victims after the terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Aurelien Meunier/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People gather at Place de la Bourse in support of the victims after the terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Aurelien Meunier/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People gather at Place de la Bourse in support of the victims after the terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Aurelien Meunier/Getty Images)
People bring flowers and candles to mourn at the Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)
BRUSSELS, BELGIUM - MARCH 22: People light candles at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People hold up a banner as a mark of solidarity at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: Candles are lit at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)
People bring flowers and candles to mourn for the victims at Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)
People mourn for the victims at Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)
A placard reads 'Share your love' at a makeshift memorial following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
Writing on the asphalt reads "More stars in Brussel's heaven" at Place de la Bourse in the center of Brussels, where people write hundreds of messages on the ground to remember the victims of Tuesday's attack, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)
A woman reads messages written on the ground at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
People walk over messages written on the ground at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
People leave candles and flowers in tribute to victims of triple bomb attacks in front of the stock exchange building in the city center of Brussels on March 22, 2016. A series of apparently coordinated explosions ripped through Brussels airport and a metro train, killing at least 26 people in the latest attacks to target Europe. / AFP / Belga / NICOLAS MAETERLINCK / Belgium OUT (Photo credit should read NICOLAS MAETERLINCK/AFP/Getty Images)
People leave messages and flowers in tribute to victims of triple bomb attacks in front of the stock exchange building in the city center of Brussels on March 22, 2016. A series of apparently coordinated explosions ripped through Brussels airport and a metro train, killing at least 26 people in the latest attacks to target Europe. / AFP / Belga / NICOLAS MAETERLINCK / Belgium OUT (Photo credit should read NICOLAS MAETERLINCK/AFP/Getty Images)
People gather around a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
A placard reads share your love next to flowers and candles laid on the ground following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
A man looks at flowers and messages outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Geert Vanden Wijngaert)
A woman places candles in the shape of a heart outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Geert Vanden Wijngaert)
Solidarity messages are written in chalk outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Geert Vanden Wijngaert)
A heart in the colours of the Belgian flag is taped onto a bag as people gather around a makeshift memorial following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
People write messages on the ground at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
A man writes the word 'Peace' in different languages at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
Two people write solidarity messages in chalk outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Geert Vanden Wijngaert)
A man walks by solidarity messages written in chalk outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Geert Vanden Wijngaert)
A replica of the Manneken Pis statue stands at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
People hold hands as they gather at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
People hold hands as they gather at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
People light candles at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
A replica of the Manneken Pis statue is placed among candles at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARD / AFP / KENZO TRIBOUILLARD (Photo credit should read KENZO TRIBOUILLARD/AFP/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: People walk across slogans written on the ground in chalk saying 'Brussels, Belgium, Today' at Beursplein sqaure following todays attack on March 22, 2016 in Brussels, Belgium. At least 34 people are thought to have been killed after Brussels airport and the Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. on March 22, 2016 in Brussels, Belgium. (Photo by Alexander Koerner/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: A painting is left as a tribute at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: A message is written on a wall following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: Flowers are placed into the mouth of a lion statue as people gather to leave tributes at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)
BRUSSELS, BELGIUM - MARCH 22: A candle is lit as people gather to leave tributes at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)
A man lights a candle next to the iconic statue of Manneken Pis outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Geert Vanden Wijngaert)
A memorial to attack victims with a Belgian flag and flowers is set up outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Geert Vanden Wijngaert)
of
SEE ALL
BACK TO SLIDE
SHOW CAPTION +
HIDE CAPTION

So why hasn't ISIS targeted the U.S. more directly?

A combination of factors explains why the U.S. hasn't been hit by a Brussels-style assault, experts say.

The most obvious factor is the U.S.'s "huge national security apparatus," Robert McFadden, retired special agent with the Naval Criminal Investigative Service (NCIS), told Mashable by phone from Washington.

Patrick Skinner, director of special projects for the New-York based Soufan Group and a former CIA case officer specializing in counterterrorism issues, hailed the U.S.'s "very strong border security."

Skinner also said the FBI "does a great job of disrupting [terror] plots early."

"Europe didn't do that for a long time. So they got these clusters," he continued, referring to the Brussels suburb of Molenbeek, which has become the center of attention for counterterrorism officials in recent months. Several of the Paris attackers were born in or resided in the area, and last week police found and arrested the last living one holed up there.

The U.S. simply doesn't have any such areas that are openly known as havens for terrorists, McFadden said.

Skinner said: "We don't have that level of extremism in the U.S. For all our faults, we haven't reached that critical mass."

SEE ALSO: Questions about airport security after Brussels attacks

But both McFadden and Skinner pointed to one major factor that stands out among the others: the huge number of European foreign fighters within ISIS's ranks.

The highest number per capita of European foreign fighters who have joined ISIS in Syria and Iraq are from Belgium, including many from Molenbeek, according to the Soufan Group, which for years has tracked their movements. Thousands more come from other European countries.

The number of Americans trained by the extremist group is only in the dozens, and none of them appears to have returned home.

Meanwhile, many of those originally from Europe have returned to their home countries after training with ISIS.

And then there are ISIS supporters who never left home, but who have been radicalized by the ones who did and came back.

"If you get 15 bad guys who stew in their radicalism, that's enough" to create a cell capable of carrying out a deadly attack, Skinner said.

Skinner and McFadden also cite another factor that has kept the U.S. from falling victim to a large-scale terrorist attack in recent years: luck.

"The truth is, we've been lucky we haven't had attacks on this scale. The very essence of terror is it's a sucker punch," McFadden said. "It's almost like we don't like to talk about it at times because we don't want to jinx ourselves. But it could happen anytime."

More from Mashable:
10,000 angry cabbies brought Jakarta to a standstill
Nixon's war on drugs: Disaster? Yes. Political vendetta? No.
Master your Mac with these tricks and shortcuts you didn't know you needed

Read Full Story

People are Reading