The African country the suspected Berlin market attacker was from has become a breeding ground for ISIS

The prime suspect in the German Christmas market attack was from a north African country that has become a breeding ground for extremism and is one of the top exporters of jihadists.

Tunisia was once thought to be an Arab Spring success story - it was called the "sole democratic success" of the uprisings that swept the Middle East starting in 2010.

But the country has been struggling with an extremism problem that was exacerbated with the arrival of the terrorist group ISIS, which has attracted thousands of Tunisian recruits. A 2015 study by The Soufan Group, a strategic security firm, found that Tunisia supplied more foreign fighters to ISIS than any other country, between 6,000 and 7,000 as of October of that year.

One Tunisian ISIS supporter drove a truck through a Christmas market in Berlin earlier this week, killing 12 people and injuring dozens more, according to authorities. Tunisia native Anis Amri, who was killed in a Friday shootout with police, was German authorities' prime suspect in the attack. Officials had been investigating Amri, but after surveilling him for months, they couldn't find any evidence of a specific plot.

ISIS claimed credit for the attack.

Amri left Tunisia for Italy after the 2011 revolution. He arrived in Germany in July 2015, but his application for asylum was rejected this June.

He had a criminal history - he spent time in an Italian prison for setting fire to a school and was known to be a small-time drug dealer - and reportedly tried to buy a gun from a German informant earlier this year. He was also thought to have had contact with a suspected ISIS recruiter who was arrested in November.

Amri's story was similar to that of other Tunisians who have joined jihadist groups.

George Packer, a staff writer for the New Yorker, visited Tunisia earlier this year to investigate the spread of extremism there.

He explained: "Before the revolution, Tunisia had been kept rigidly secular. Now the black flag of radical Islam flew over many buildings, and hard-liners known as Salafis - the word refers to the original followers of the Prophet Muhammad - took advantage of the new openness and tried to impose Sharia in their neighborhoods."

When Tunisia cracked down on these Salafis, they simply went underground, according to Packer.

And with a nearby ISIS outpost in neighboring Libya, young people with few options for a prosperous future in Tunisia feel that traveling to join the terrorist group could lead to a better life for them.

An unemployed telecommunications engineer, Nabil Selliti, said he joined ISIS because it offered him opportunities in his career field, according to the New Yorker.

"I can't build anything in this country," he said. "But the Islamic State gives us the chance to create, to build bombs, to use technology."

Some young people in Tunisia feel that the revolution did not significantly improve their lives. One young person lamented to Packer that "the rich in Tunisia get richer, and the poor get poorer."

And terrorist attacks inside the country have hurt Tunisia's tourism industry, which previously provided thousands of jobs and accounted for 8% of the country's GDP, according to Reuters.

Henry Wismayer visited Tunisia earlier this year for Vice to look into how a major terror attack on a beach and hotel had affected the country.

He explained: " The abrupt decline of Tunisia's tourist industry, many say, feels like a betrayal of the optimism that accompanied the Arab Spring in 2011. ... Tunisia's new-found pluralism has turned it into a target for extremists, hell-bent on creating an Islamic world under the boot heel of Sharia law."

Still, not every Tunisian ISIS supporter is compelled to join a terrorist group because of poverty or lack of opportunity. ISIS' core ideology seems to hold appeal for some, even those who have means.

A 27-year-old architecture student, Ahmed Amine Jebri, told Yaroslav Trofimov of The Wall Street Journal earlier this year that "so many people have left from here, and quite a few of them were rather well-off."

"Some in the neighborhood believe these guys are fools who had gone to Syria to get killed," he said. "But many others say they are now in paradise with the virgins."

Moncef Marzouki, a human-rights activist who was democratic Tunisia's first president from 2011 to 2014, told the Journal that popular disappointment is spreading in Tunisia.

"It's not the matter of tackling socioeconomic roots," he said. "You have to go deeper and understand that these guys have a dream - and we don't. We had a dream - our dream was called the Arab Spring. And our dream is now turning into a nightmare. But the young people need a dream, and the only dream available to them now is the caliphate."

Jake Kanter contributed to this report.