General McChrystal wrote an article that appeared in Foreign Policy:
Like all too many military forces in history, we initially saw our enemy as we viewed ourselves. In a small base outside Baghdad, we started to diagram AQI on white dry-erase boards. Composed largely of foreign mujahideen and with an overall allegiance to Osama bin Laden but controlled inside Iraq by the Jordanian Abu Musab al-Zarqawi, AQI was responsible for an extremely violent campaign of attacks on coalition forces, the Iraqi government, and Iraqi Shiites. Its stated aim was to splinter the new Iraq and ultimately establish an Islamic caliphate. By habit, we started mapping the organization in a traditional military structure, with tiers and rows. At the top was Zarqawi, below him a cascade of lieutenants and foot soldiers.
But the closer we looked, the more the model didn't hold. Al Qaeda in Iraq's lieutenants did not wait for memos from their superiors, much less orders from bin Laden. Decisions were not centralized, but were made quickly and communicated laterally across the organization. Zarqawi's fighters were adapted to the areas they haunted, like Fallujah and Qaim in Iraq's western Anbar province, and yet through modern technology were closely linked to the rest of the province and country. Money, propaganda, and information flowed at alarming rates, allowing for powerful, nimble coordination. We would watch their tactics change (from rocket attacks to suicide bombings, for example) nearly simultaneously in disparate cities. It was a deadly choreography achieved with a constantly changing, often unrecognizable structure.
Over time, it became increasingly clear -- often from intercepted communications or the accounts of insurgents we had captured -- that our enemy was a constellation of fighters organized not by rank but on the basis of relationships and acquaintances, reputation and fame. Who became radicalized in the prisons of Egypt? Who trained together in the pre-9/11 camps in Afghanistan? Who is married to whose sister? Who is making a name for himself, and in doing so burnishing the al Qaeda brand?
All this allowed for flexibility and an impressive ability to grow and to sustain losses. The enemy does not convene promotion boards; the network is self-forming. We would watch a young Iraqi set up in a neighborhood and rise swiftly in importance: After achieving some tactical success, he would market himself, make connections, gain followers, and suddenly a new node of the network would be created and absorbed. The network's energy grew.