Handout shows U.S. journalist James Foley speaking at Northwestern University's Medill School of Journalism, Media, Integrated Marketing Communications in Evanston, Illinois
U.S. journalist James Foley speaks at Northwestern University's Medill School of Journalism, Media, Integrated Marketing Communications in Evanston, Illinois, after being released from imprisonment in Libya, in this 2011 handout photo provided by Northwestern University. REUTERS/Tommy Giglio/Northwest

More than retaliation for the recent US airstrikes, ISIS released for all the world to see the beheading video of American journalist James Foley to attract more recruits into the cause.

Moreover, the execution, the ISIS' first direct terrorist attack against the U.S., meant to carry the message the group is not afraid of the world superpower.

Barbaric it may seem, but the release of the video was part of a well-oiled propaganda machinery by the ISIS to recruit members, more especially foreign members.

"They [Islamic State militants] believe these actions serve them," Scott Stewart, vice-president of tactical analysis for the geopolitical intelligence firm Stratfor, told CBC News.

Proof of that success is that despite the "barbaric displays," the group continued to grow in numbers and strength.

For months, the ISIS has beheaded, amputated and crucified thousands of people in places they control in Syria. "It's been successful. They've been able to grow and flourish, and they have been able to attract people to their cause despite this barbarity," Stewart said.

It's been reported that their membership reach has greatly expanded to include foreign nationals, even Americans and west Europeans.

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Mike Morell, former deputy CIA chief, said those foreign members can anytime wreak havoc, particularly in the United States, to conduct small-scale attacks. "If an ISIS member showed up at a mall in the United States tomorrow with an AK-47 and killed a number of Americans, I would not be surprised," Morell told 'CBS This Morning.'

Morell said this is the most opportune time to strategise against the militant group. He believed the release of James Foley's beheading video aimed to intimidate the United States into backing off of the attacks it had done the last several weeks

"The definition of terrorism is violence for political effect," Morell said. "We should mark this date down because this is ISIS' first terrorist attack against the United States."

Stewart echoed Morell's thoughts that the group thinks they are intractable.

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"They believe that basically they are undefeatable. They believe that Allah is favouring them, so they believe they can be this brazen."

Morell believes the ISIS will indeed assassinate Steven Sotloff, another American journalist identified at the end of James Foley's beheading video. Like Foley, Sotloff was also seen wearing an orange jumpsuit.

"We need to keep moving forward with our policy. We cannot let something like this stop us," Morell stated.