Most of today’s activist class in the West either have no knowledge of — or choose to forget — one of the bloodiest internal conflicts in the modern Arab world: Algeria’s war against the Islamic Salvation Front (FIS), an offshoot of the Muslim Brotherhood.

After the FIS won the first round of parliamentary elections in 1991, the Algerian military intervened. What followed was a decade-long civil war — Algeria’s “Black Decade” — that left more than 200,000 people dead, many of them civilians.

This was not a remote or tidy struggle. It was marked by massacres of entire villages such as Rais, Bentalha, and Sidi Hamed, where men, women, and children were slaughtered.

Armed Islamist factions used children as human shields. The state responded with mass arrests, secret detention camps, torture, and widespread disappearances. Human rights groups estimate that 7,000–20,000 Algerians simply vanished after being picked up by the security services. It was a conflict of unrelenting terror that scarred Algerian society for a generation.

This was not an isolated episode in the Arab world. Across the Middle East and North Africa, secular Arab governments have repeatedly been forced to crack down on the Muslim Brotherhood when it has threatened to seize state power. Egypt, Syria, Jordan, the Persian Gulf states (except Qatar), and of course Algeria have all confronted the movement. In each case, the lesson has been the same: when the Brotherhood is allowed to operate unchecked, the consequences are catastrophic for civil society, women, minorities, and political pluralism.

Indeed, the Brotherhood’s goal is not limited to establishing a caliphate in Muslim-majority states; it is openly global. Over the past half-century, it has branched out to more than 80 countries and embedded itself deeply within Western societies — particularly in the United Kingdom, where it enjoys a level of freedom and legitimacy through its umbrella proxies that it does not have in much of the Arab world.

The Brotherhood’s well-funded network of charities, student groups, and NGOs provide not only social services but also a political infrastructure for the movement’s ideology. These networks have helped it to recruit and expand its influence among Muslim communities worldwide and to penetrate Western institutions — from universities and local councils to lobbying organizations, media outlets, and even the church institutions.

Yet Western elected representatives, with few exceptions, continue to treat the Brotherhood as if it were simply a conservative religious charity movement. Some even partner with its front groups under the banner of “community engagement” or take part in their “interfaith dialogue” panels. This is a profound strategic error. The Brotherhood’s long-term aim is to reshape societies from within, incrementally eroding the Western liberal democratic norms that have helped the West flourish.

Despite a series of extensive and well-publicized inquiries — most notably the UK government’s internal review commissioned by David Cameron — the proscription of the Muslim Brotherhood was abruptly shelved without any clear explanation. Led domestically by Charles Farr and internationally by Sir John Jenkins, the review described the Brotherhood as “a possible indicator of extremism” and criticized the secrecy of its operations in Britain, highlighting concerns over its fundraising, membership structures, and influence in student groups and community organizations. Yet, despite these stark findings, the process fizzled out into nothing more than warnings, vague descriptors, and policy recommendations. More than a decade later, no decisive action has been taken to proscribe the group, and no substantive update has been issued.

In the US, officials like Tom Cotton and Marco Rubio were leading voices in pushing for the Muslim Brotherhood to be designated a terrorist organization under US law. Cotton, along with other Republicans, has introduced legislation and sent letters calling on agencies like the IRS to investigate Muslim Brotherhood–linked groups such as CAIR for their nonprofit status, alleging financial ties to extremist causes.

The West’s failure to take this challenge seriously represents a grave danger. As Algeria’s bloody decade showed, ignoring the Brotherhood’s true nature does not lead to coexistence but to chaos and bloodshed.

Right now, Israel is engaged in a war against Hamas, another offshoot of the Muslim Brotherhood, and a serious existential threat to the Jewish State. Unlike the other Arab states that were forced to crack down on the Muslim Brotherhood without fear of international condemnation, Israel is trying its best to conduct an ethical war. Yet it faces an unprecedented international backlash that other Arab states did not face — not just from naïve activists, but even from the Western elected leaders.

Western policymakers must learn from the experience of those countries that have already paid the price of underestimating this movement, before it is too late.

Investigative Project on Terrorism (IPT) Senior Fellow Potkin Azarmehr is a London-based investigative journalist, business intelligence analyst, and TV documentary maker who was born in Iran. He regularly contributes to several newspapers and television stations on Iran and Middle East related news. You can follow him on Twitter @potkazar. A different version of this article was originally published by IPT.