David Kilcullen: It's different in three major ways. Firstly, it is much bigger and more militarily capable than al-Qaida ever was. It has tanks, it has helicopters, it's got very large numbers of artillery pieces, it's got more than 30,000 fighters, so it's significantly larger and more militarily capable. Secondly, it controls about a third of Iraq and about a third of Syria, including a network of very connected cities, economic installations that make it about between $2 million and $3 million a day in terms of revenue, and it's really building a significant territorial state in the Middle East, which is something that al-Qaida was never able to do. Thirdly, and, actually, I think most importantly for people in Australia and New Zealand, it's having a very significant reinvigorating effect on regional groups in South-east Asia, in Africa and the Middle East. That's really taking us back almost to square one in terms of re-energising a global jihad against the West. So I think all those three things adding up together, it's really a very, very significant threat that's somewhat larger than what we've really ever seen from al-Qaida.