According to Anders Thornberg, the leader of Sweden’s security service, Säpo, there are now as many as 2,000 Islamic extremist sympathizers in the Nordic nation. That is a 900% increase from just seven years ago, when the number was estimated to be approximately 200.

Thornberg says he has “never seen anything like it before.”

Despite the belief that the great majority of radical sympathizers lack the ability and means to conduct terrorist attacks, such an increase is deeply concerning.

“Thornberg said Säpo now receives around 6,000 intelligence tips a month concerning terrorism and extremism, compared to an average 2,000 a month in 2012,” reports The Local.

The Local also quotes “terror expert” Magnus Ranstorp, who outlines four reasons the threat is growing so rapidly.

First, conflicts in the Middle East are helping foment extremism; second, online propaganda is being used brilliantly by the Islamic State and other extremist organizations to influence and recruit fighters; third, Sweden’s “vulnerable areas,” in which there are higher levels of poverty and crime, allow extremists to recruit relatively unnoticed; fourth, “prevention measures have been pretty tame,” notes Ranstorp. “It's become better in the last year, but I have long said that if you compare Denmark and Sweden, Denmark is at university level and Sweden at kindergarten level.”

Agence France-Presse (AFP) reports that of the roughly 300 Swedish individuals who have left the country to join extremists in the Middle East, nearly 150 have “returned or are in the process of returning home.”

Worse, some municipalities in the Nordic nation are welcoming fighters back with open arms. According to Newsweek: “Sweden is one the best countries for a foreign fighter to return if they want to reintegrate. It is trialling a rehabilitation programme that gives Swedish extremists housing, employment, education and financial support. Anna Sjöstrand, the municipal coordinator against violent extremism in the city of Lund, said in October 2016 that it is much cheaper to reintegrate someone than to abandon them.”

Some of the men who traveled to Syria and elsewhere claim they were fighting against ISIS and other extremists, but those claims are suspect at best, and almost impossible to verify — and these men are being allowed back into Sweden.

In an attempt to prevent a similar crisis in the United States, several politicians, most notably Senator Ted Cruz (R-TX), have attempted to remedy the situation through legislation that would strip the citizenship of anyone who goes overseas to fight with extremist organizations. Cruz’s bill has so far failed to gain enough traction.

Europe has seen a staggering increase in Islamic terror attacks over the last several years, as shown by this chart from Vision of Humanity’s Global Peace Index:

Radical Islamic ideology is spreading like a cancer; organizations like the Islamic State are recruiting vulnerable individuals through methods not previously used. Their methodology is working, as evidenced by the shocking increase in radical Islamic sympathizers living in European nations in 2017 as compared to 2010.

If Europe and the United States allow this trend to continue unabated, seemingly content to ignore it, hundreds will become thousands, and thousands will become tens of thousands. Then terror won't be the exception, but the norm.