No Article Five for Europe

Article Five of the North Atlantic Treaty reads, “an armed attack against one or more [members] in Europe or North America shall be considered an attack against them all.” Under this agreement, each of the attacked state’s allies are obligated to assist with “such action as it deems necessary, including the use of armed force.” Given the recent attacks on Paris and now Brussels, it initially seems reasonable to categorize these attacks under Article Five; however, political and military strategy makes such action unnecessary and possibly harmful to NATO’s mission.
Only once in history has NATO invoked Article Five—on September 12, 2001, in direct response to the attacks on the World Trade Center. The invocation immediately drew NATO into the fight against terrorism; NATO immediately increased the ability of member states to share military intelligence as well as use each other’s airfields and airspaces for launching military operations. In addition, a December 2001 ordinance by the UN established the International Security Assistance Force, an international coalition for security operations in Afghanistan. NATO took control of ISAF in 2003 until its withdrawal in 2014. Under NATO command, ISAF grew to a total size of 130,000 soldiers.
NATO member states had been engaging in their own operations independently until September 2014 when the alliance, at the urging of the United States, decided to take collective action against ISIS. However, so far, NATO contributions to the battle against ISIS have been limited to flying support aircrafts for allied members and providing supplies to local militias. Airstrikes have only been conducted independently by member states, with the United States undertaking the overwhelming majority of the sorties.
And even after the much deadlier Paris attacks in November 2015, France declined to invoke Article Five out of pragmatism: it would be a call to arms for allies that were already engaging in their own independent bombing operations. Likewise, it was unlikely that such an invocation would change the involvement of other member states, as they would have been free to commit only those resources that they felt were required. Even without the heavy hand of Article Five, some other members increased their aid independently. For example, Germany approved a measure upscaling counter-ISIS operations within a month after the attacks.
NATO’s strategy against ISIS is fundamentally different from the one it used to combat al-Qaeda in Afghanistan. The mission in Afghanistan was to remove the ruling Taliban from government to deny al-Qaeda an area of safe operations. Now, the goal is simply to destroy ISIS, and various military groups (although no NATO members) are already engaged in ground combat toward that end, reducing the immediate necessity of a collective Western retaliation. Obama has expressed skepticism about sending infantry to the region, a much costlier proposition compared to the current status quo of bombing runs and supply drops.
Most importantly, invoking Article Five would provide propaganda and legitimacy to ISIS, a state which thrives off of recognition and social media presence. It would grant ISIS the same level of recognition and notoriety as al-Qaeda gained in 2001 for an attack much smaller in scale and damage.