Thomas H. Kean and Lee H. Hamilton

Fifteen years after the Sept. 11 attacks, the battle against terrorism is far from over. The threat we face today is arguably worse than the one we confronted in 2001.

Certainly, we have not suffered another catastrophic attack on the scale of 9/11 thanks to considerable progress in reforming how we protect the homeland. Intelligence sharing among federal agencies as well as with their state and local counterparts, sorely lacking before 9/11, is now the norm. Commercial aviation, ports and other critical infrastructure are better protected. The thousands of people involved in protecting the country deserve our gratitude.

Even so, we have been unable to prevent all terrorist attacks in the United States. Globally, terrorism has also intensified. According to the Global Terrorism Index, terrorist activity reached its highest recorded level in 2014, the last year with available data, with 32,685 terrorist-caused deaths. In 2001, that figure barely exceeded 5,000. Out of 162 countries studied, 93 have suffered a terrorist attack.

These are not just the internal problems of distant lands. Our focus cannot solely be on our own homeland. Terrorism might not pose an existential challenge to the United States, but it is a spreading disease eating away at the foundation of the free, open and lawful international system and the alliances that the U.S. depends on for its prosperity and security.

Terrorist-fueled instability cascades across borders and jumps across oceans. It aggravates ethno-sectarian tensions, fuels conflicts, displaces millions, and weakens governments. Terrorists target public spaces, international air travel and cyberspace, while seeking weapons of mass destruction. Terrorism’s toll on our homeland, on the vibrant democracies of our European allies, on the stability of our Middle Eastern partners, and on the security of the global commons is alarming. Even when America is not the target, terrorism is a strategic threat we must confront.

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The approach of the past 15 years, dominated by military counterterrorism operations, will not suffice. In the 9/11 Commission Report, we warned that terrorism would “menace Americans and American interests long after Osama bin Laden and his cohorts are killed or captured.” We stressed that our strategy “must match our means to two ends: dismantling the al-Qaeda network and prevailing in the longer term over the ideology that gives rise to Islamist terrorism.” We have yet to match our military might with an equal focus on the ideological aspects of the struggle. Until we do, this threat will not diminish.

Advanced by deft use of the media, deeply rooted organizations, exploitation of economic and political grievances, and with support from certain governments, the ideological landscape of the Muslim world is inundated with extremist narratives. These radical perversions of Islam might not condone violence, but they crowd out mainstream, tolerant and pluralistic ideas. The prevalence of even non-violent extremism can also acclimate communities to the siren song of terrorism.

The evidence of this link between extremist beliefs and terrorism is ample. A British government review of the Muslim Brotherhood found that, while the group itself might not be involved in terrorism, “both as an ideology and as a network it has been a rite of passage for some individuals and groups who have gone on to engage in violence and terrorism.”

Similarly, we found in the 9/11 Commission Report that Saudi government funding “to spread Wahhabi beliefs throughout the world, including in mosques and schools (has) been exploited by extremists to further their goal of violent jihad against non-Muslims,” while in Pakistan, religious schools “have been used as incubators for violent extremism.”

As long as extremist voices persist in Muslim societies, the distance between socially acceptable beliefs and violence will always be far too short.

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The United States cannot and should not impose our way of life or system of government on other countries. Nonetheless, we can and must use all the elements of national power — diplomatic, economic, cultural, informational and technological — to proclaim our values. We must empower those who also believe in the rule of law, freedom, tolerance for diversity and broadly shared economic prosperity. This effort cannot solely come from America. In order to prevail in the struggle, we will need the help of Muslim allies and communities.

Fifteen years is too long to wait to get our strategy right. We cannot risk another decade-and-a-half of policies that do not reduce the terrorist threat. That is why we are convening a task force of experts to develop a long-term strategy to combat terrorist ideology. Changing the worldview of societies is a long and difficult process, but it provides the only hope of quelling the terrorist threat.

The post-9/11 era has now spanned two terms each of both Republican and Democratic administrations. The challenge of keeping our country safe will be inherited by whomever is elected president in November. A bipartisan approach will be essential; no one political party has a monopoly on the talent, imagination or ideas necessary to defeat our terrorist enemies.

On Sunday, we remember the nearly 3,000 innocent Americans who were murdered on Sept. 11, 2001, and the thousands of Americans who have given their lives and been wounded in defense of our country in the years since. In the weeks immediately after the 9/11 attacks, our country came together in its determination to defeat that enemy. Reigniting that unity of purpose will honor those who are gone and help provide the surest way forward to prevail in the ongoing struggle.

Former governor Thomas H. Kean and former congressman Lee H. Hamilton served as chairman and vice chairman, respectively, of the 9/11 Commission. They are co-chairs of the Bipartisan Policy Center’s National Security Program.

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