Excerpt:

Just like any other bureaucracy, such groups have clearly delineated hierarchies, internal rules and divisions of responsibility. That clarity means it is easy to replace a leader with a deputy. It also makes the organization stable: If one cog falls out, the rest of the machine can still function. For a group as large and complex as the Islamic State, the infrastructure is simply too large for any one person, even a top leader, to make or break its future. This is why terrorism scholars have repeatedly concluded that killing or capturing terrorist leaders — a strategy known, colorfully, as “decapitation” — does not work.

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