The death of Islamic State's Abu Mohammed al-Adnani in a US (or possibly Russian) air strike has been described by some as the 'biggest ever blow to Islamic State.'

Although often identified as the group’s spokesman and chief propagandist, Adnani’s role was much more significant than that. Adnani was one of the group’s first foreign fighters and longest-serving members, having joined the nascent group in 2000. If reports are to be believed, he was even being groomed as a successor to Islamic State leader Abu Bakr al-Baghdadi.

This is not to underestimate the importance of his role as spokesman. While his messages are unlikely to have the radicalising resonance of Anwar al-Awlaki, Adnani’s blunt missives against the West made an impact. Take, for example, Adnani’s call in 2014 for Islamic State supporters to 'smash his head with a rock, or slaughter him with a knife, or run him over with your car…' and the wave of unsophisticated but deadly attacks over the past two years, culminating in July’s truck attack in Nice.

Yet Adnani’s significance goes beyond his ability to recruit and legitimise the violence of disparate individuals and groups across the world. Adnani also had a hands-on role in coordinating and directing terrorist attacks outside of Iraq and Syria, most notably in Paris last November. As the Pentagon indicated, he was the ‘principal architect’ of Islamic State external operations.

How then should we expect Islamic State to respond to the death of an individual of Adnani’s seniority and importance? In the short-term, its reaction may have both positive and negative counter-terrorism consequences.

Given its size and bureaucratic nature, we should expect Islamic State to have a succession plan in place, and a relatively large number of individuals with operational and leadership experience to choose from. But Adnani is no ordinary leader. His eventual role encompassed communications and propaganda, oversight of external operations, membership of the Shura council, and a role as provincial governor. And despite the depth of Islamic State’s organisation, it has suffered numerous losses across the leadership ranks over the past few months. Adnani may not be replaceable by one individual, and there are no guarantees that his replacements will be of similar calibre. The US will hope that this process will force the organisation to turn inwards and lead to a short-term reduction in capability and focus.

Despite this, what we know about Islamic State suggests that Adnani’s death might not immediately reduce the terrorist threat. As I wrote three weeks ago, the external operations network directed by Adnani reportedly has numerous operatives in place in Europe and beyond. We have already seen predictable calls for revenge by Islamic State supporters online. And if the identity and approach of Adnani’s replacement in this role is uncertain, a terrorist attack would be a logical way for Islamic State to reassure friends and foe alike that their threat has not diminished.

Questions will undoubtedly be asked if the death of Adnani appears to trigger further terrorist attacks. But if Adnani’s death impacts the short-term focus of the network (for better or for worse), it will not be the root cause of the threat it poses. Islamic State has prioritised terrorist attacks in the Middle East, Europe and beyond over the past two years and would have continued to do so, regardless of Adnani’s status.

Beyond the short term, the impact of Adnani’s death on the threat picture is less certain.

Adnani is the latest in a long line of terrorist leaders to be killed in US air strikes. The list includes al-Bagdhadi’s predecessors as head of Islamic State, Osama Bin Laden, and numerous other senior Al Qaeda leaders. As with the others on this list, predicting how Islamic State might have behaved had Adnani survived yesterday’s drone strike is a largely academic exercise for alternate historians. There are far too many moving parts. What we have learned is that the fear of future drone strikes does impact on the ability of terrorist networks to communicate and coordinate their activities, and that finding candidates to replace charismatic and experienced leaders like Bin Laden or al-Awlaki is no easy task. 

Despite these difficulties, Islamic State, the Al Qaeda global brand and Al Qaeda in the Arabian Peninsula have been able to flourish after the death of senior leaders. Drone strikes are a tactic, not an holistic counter-terrorism strategy. They cannot on their own be expected to counteract the impact of broader world events.

Adnani’s death is significant; reducing the talent available to a terrorist group does affect its capability. But it represents a small victory in a much larger war. The success or failure of the Islamic State project is likely to depend on much bigger geopolitical developments than the fate of individual personnel.