Allen, who just left the post, told The Associated Press it`s worth remembering the magnitude of the work it took previously to defeat a force in Iraq smaller than IS following the U.S. military surge that played a role in driving out al-Qaida in Iraq — a precursor to the IS group. He said the U.S. could insert a few brigades or try to empower local forces that will lead to a long term solution.

Allen`s remarks come ahead of Canada`s annual Halifax International Security Forum.

"You can go big and you can go with Western forces or you can try to empower the indigenous forces to defeat Daesh and that in fact brings you the long term solution and not being faced with a crisis ultimately of having to pull your own forces out and having not prepared the kinds of forces necessary to hold and that`s a really important point, and it`s often missed in this conversation," Allen told the AP in a telephone interview from Virginia.

Allen said they`ve had success containing IS in Iraq and Syria but said more attention needs to be spent on the expansion of IS with its terrorist allies like Boko Haram in Africa and with Westerners who are either inspired or directed by the IS core in Syria and Iraq.

"The displaced foreign fighter, who has departed the battle space, or a foreign fighter who has been recruited locally and is serving the role of a foreign fighter in attacks domestically, this is something that we need to really concentrate on," Allen said.

"This is not just about bearing down on Daesh in Iraq or Syria. This is about understanding the network and being able to as a community of nations, and in support of France, to bear down on that aspect of the conflict."

He said global attention on the problem following the Paris attacks will help allies begin to understand what`s needed to defeat IS. He called the Halifax forum one of the premier security conferences and said it provides an enormous opportunity to discuss possible solutions.

In its seventh year, the forum attracts top defense and security officials from Western democracies. About 300 people gather each year in an intimate setting at Halifax`s Westin hotel. Robert Work, U.S. Deputy Secretary of Defense, Canada`s new defense minister, Harjit Sajjan, and Admiral Michael Rogers, Director of the U.S. National Security Agency, are among the speakers.

"Everyone knows now that this is something that must to be defeated," Forum President Peter Van Praagh said of IS. "The question now is what are the best tactics to do this? Is it from the air? Do we need ground troops? Are local forces going to be enough to do it?"

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