When President Barack Obama arrived at the North Atlantic Treaty Organization summit in Wales, he found a room full of member states that are focused on the original purpose of NATO: to provide a collective defense against the grave threat of Russian expansion. But the president must recognize that today’s threats are more complex than those of 1949, the year of NATO’s founding. NATO and its member countries are not only threatened by the prospect of war from the East, but also by a growing and dangerous new enemy on its southern flank — the terrorist group known as the Islamic State of Iraq and al Sham, or ISIS.

NATO and other multinational alliances were built on certain mid-20th century assumptions — that generally, the laws of war would be followed, and conventional military power would deter conventional military power. And for decades, most NATO states viewed terrorism as a domestic matter to be dealt with inside their own borders.

But ISIS and similar groups don’t play by the traditional rules of war. ISIS erases national borders, taking a bulldozer to the Iraq-Syria border. They kill civilians, kidnap Westerners for ransom, and behead journalists. They also harness the power of social media — unimagined at NATO’s creation — to recruit disaffected youth in the West to their cause. Above all ISIS is a threat to all 28 NATO member states.

ISIS’ fight against the Assad government in Syria has now spilled over into Iraq, threatening the stable Kurdish areas in the north and raising concerns about the security of Baghdad itself. As Islamist militants spread in the region, NATO states are reacting to the current events and responding. The United Kingdom raised its threat level based on the conflict in Syria and Iraq. Germany is sending weapons to arm Kurdish forces against ISIS. France and Saudi Arabia are jointly sending $3 billion worth of weapons to Lebanon to prevent ISIS’ advance there.

Terrorist groups like ISIS are not easily defeated, and NATO’s response to this threat must be proactive. Up to this point, NATO’s counterterrorism missions have been reactive to terrorist attacks and shaped by events, arguably piecemeal and put together out of existing military capabilities.

ISIS poses a provocative threat to NATO’s member states which is why the alliance’s commitment to its core mission “to safeguard the freedom and security of its members through political and military means” is more important than ever. Terrorism like that of ISIS threatens our freedoms.

NATO needs to develop clear principles and capabilities to address terrorist groups that threaten regional stability. At the 2012 NATO Summit in Chicago, the member states issued policy guidance on counterterrorism that referenced the unique counterterrorism capabilities that NATO members have developed since the horrific events of Sept. 11.

And currently, Secretary of State John Kerry is properly aligning various member nations to use military, economic and political tools to degrade and disrupt ISIS. But this cooperation needs to be formal and robust — built on a NATO-like infrastructure of operational command, cooperation and communication.

Beyond building the tools, NATO members must reach consensus on how this new, more emboldened capability should be used. They should consider questions like: What’s the trigger for NATO counterterrorism engagement? What would the goals be of such an engagement? What would be the accompanying tools for political reform to prevent terrorist groups from re-emerging?

From its inception NATO and other treaty organizations have generally — though not flawlessly — deterred and disrupted severe threats. Today’s threats are radically different from yesterday’s. Our responses should be as well.

Rep. Steve Israel is a Democrat from New York. Mieke Eoyang is the Director of the National Security Program at Third Way, a centrist Democratic think tank.