In the southern Philippines city of Marawi, militia groups aligned with IS have been in control for months.
Now, the Philippine government is trying to retake the city by slowly killing off enemy soldiers and seizing guns.
But the director of the Jakarta-based Institute for Policy Analysis of Conflict, Sidney Jones, says the signs of a rising, organised terrorism threat had been obvious for a while.
"And in some ways, if we had read the signals properly, we might have seen that they were actually in the process of building up something increasingly complex and increasingly big."
In November 2016, IS-affiliated Maute rebels took over a small town on the island of Mindanao.
Ms Jones says, in retrospect, it was clearly a trial run for what would later happen in the city of Marawi.
"All this time, the Philippine security authorities didn't see anything particularly amiss. To them, this was just another same-old, same-old insurgent group, splinter group. (They thought,) 'Yes, they have guns, but everybody has guns in the Philippines. Yes, they were stockpiling weapons, but everybody does that.' So there was no real sense that this was qualitatively different."
Now, more than 460 people have died since the fighting in Marawi broke out in late May after the government reportedly tried to capture a wanted leader of the Abu Sayyaf rebels.
The death toll includes more than 80 members of the security forces and more than 40 civilians.
More than a quarter of a million people have been displaced.
As the conflict continues, the Australian Defence Force's Chief of Joint Operations says Australian involvement is important.
Vice Admiral David Johnston points to the group's connection to IS, or Daesh.
"I think what's important about the events in Marawi is that it has been conducted under the banner of, in part, that influence of Daesh into the region. So that is significant as a message into the region and why the support by the Australian government to the Filipinos has been important."
There is evidence the group has strong connections with militants in Indonesia, Malaysia and wider southeast Asia.
Ms Jones says that may pose a danger to security throughout the area.
"I think there's concern on the part of everyone in the region that what's taking place in Marawi could blow back to other parts of South-East Asia and Australia through people with new combat experience coming back to their own countries and mounting actions there. Also, that there could be a new level of coordination."
However, Vice Admiral Johnston says he believes the likelihood of anything similar to the fighting in Marawi spreading further afield is minimal.
"The assessments that I've seen are that the scale of event that has occurred in Marawi at the moment is not likely to be replicated in other parts of Mindanao or outside it. So the number of fighters and weapons involved, which is significant in Marawi, (is) not likely to be seen in too many other locations."
