ISIS's online propaganda machine, in one chart

During his Sunday evening address about the San Bernardino attacks, President Obama confirmed many Americans' fears about the shooters: They were ISIS supporters, who had been attracted to kill in the group's name without any central direction. "It is clear that the two of them had gone down the dark path of radicalization, embracing a perverted interpretation of Islam that calls for war against America and the West," Obama said.

We still don't know a lot about how exactly this happened. But we do know that ISIS uses a sophisticated social media and online propaganda operation to try to reach Americans. According to a recent report on ISIS's presence in the US, this online network plays a "crucial role" in ISIS's attempts to radicalize young Americans. So if we're worried about future San Bernardino–style attacks, looking at the strength of ISIS's online network is a good place to start.

On Friday, respected terrorism scholar Aaron Y. Zelin, the creator of the widely cited jihadist primary source clearinghouse website Jihadology, did just that. In a short report for the International Centre for the Study of Radicalisation, he tallied up numbers on ISIS photos and press releases coming from ISIS in Iraq and Syria. What's interesting — aside from the fact that ISIS is putting a lot of photos and press releases on the internet — is that the pace is actually slowing. While the ISIS media machine was cranking out content at an increasing rate in early and mid-2015, they've actually started slowing down:

This chart doesn't show it, because Zelin doesn't list data month by month, but the decline in ISIS output really began in September. "There was a steady rise in photos from January-March period to the June-August period, with a drop off for every three-month category since," he explains. "[ISIS]'s much-vaunted media machine has declined over the past half-year."

So what's going on? According to Zelin, the drop-off is the direct result of ISIS's growing weakness. "I believe there may be two reasons for this decline: the killing of [ISIS] media operatives, and/or the loss in territory," Zelin writes. Indeed, there's a general consensus among experts that ISIS is losing ground, and this may simply be making it harder for ISIS to put together plausible propaganda selling its narrative of victory.

According to Zelin, evidence from both ISIS's social media accounts and the propaganda outlet suggests this is true. "Beyond the quantity of releases, the quality has diminished too," he writes. "[Terrorism analyst and expert in political and extremist uses of social media] JM Berger told me that he has anecdotally seen [ISIS] social network become less cohesive in part because of the drop in media, though he cautions there may be other factors at play."

In other words, the best strategy to disrupt ISIS's internet reach is the simplest: break up its caliphate in Syria and Iraq on the ground, by force. While weakening them at home may produce a temporary terrorist backlash abroad, it's the only way to end the threat from ISIS's online recruiting machine in the long run.

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