Two decades on from the atrocity of the Sept 11, 2001 attacks, terrorism continues to metastasise. Terrorist spectaculars like the brutal attack at Kabul's international airport - claimed by the Islamic State in Iraq and Syria - Khorasan (ISIS-K) - continue, as do attacks like those carried out by individuals inspired by ISIS ideology, the recent Auckland stabbings being a case in point.

But to properly understand and track terrorism's future evolutions, it is important to consider where we have come from, and where new expressions of the terror threat emerge from. Going forward, they will matter just as much as existing ones.