LTC David Kilcullen describes a part of the Iraq COIN strategy as an “urban tourniquet.” Walling off neighborhoods can reduce violence between sectors by reducing insurgent mobility. This functions like a tourniquet to slow blood loss.

Gated Communities are widespread in Third World Countries. The upper class literally seal off their neighborhoods from the rest of the lawless city. Armed guards patrol the perimeter and prevent the violence from spilling over.

This technique can be applied to peacekeeping to prevent two hostile populations from killing one another.

This is actually modeled by Epstein’s experiment with Civil Violence. A Safe Haven guarded by peacekeepers can stop inter-group fighting. Without guarded safe havens, the violence is unrestrained.

Kilcullen explains the general theory:

The “gated community” stops the cycle of sectarian violence in three ways.

First, it makes it much harder for terrorists to infiltrate a community. We only establish perimeter security (checkpoints, T-walls, etc.) once the area has been cleared and secured, close relations are established with the population, and we have troops on the ground securing the district in conjunction with the people. Once the gated community goes in, this makes it much harder for extremists to re-enter.

Second, the perimeter controls make it much harder for terrorists to launch attacks from within that district, because they have to smuggle a car bomb or suicide vest out, through a limited number of controlled access points. This reduces extremists’ ability to use gated districts as a base to attack neighboring areas.

Third, if the terrorists do manage to mount an attack, the security controls protect the gated community against retaliation by “death squads”. This reduces fear within the community, alienates extremists from the population (since they can no longer pose as defenders) and emboldens people, who would otherwise be too intimidated, to tip off the security forces to enemy presence.

We’ve seen much of this effect in Baghdad today. Violence against civilians is falling. The number of intelligence tips against insurgent forces is rising.

The local populations turned on occupying insurgent forces and are more willing to trust the government. The people in gated communities are turning on Al-Qaeda.

Sunni residents of a west Baghdad neighborhood used assault rifles and a roadside bomb to battle the Sunni insurgent group al-Qaeda in Iraq this week, leaving at least 28 people dead and six injured, residents said Thursday.

The mayor of the Amiriyah neighborhood, Mohammed Abdul Khaliq, said in a telephone interview that residents were rising up to try to expel al-Qaeda in Iraq, which has alienated other Sunnis with its indiscriminate violence and attacks on members of its own sect.

In this particular case, “moderate” insurgents, like the Islamic Army in Iraq and other local Sunnis, turned on their former AQI allies. They no longer fear Mahdi Militia Death Squads so they no longer view AQI as a protector.

Urban Tourniquets also help in other ways. Insurgents may still be able to communicate (via the internet or cell phones) but they lose “real-life” mobility.

Social networks need economies of scale and cooperation across a large region. They need to gather bomb material, bomb-building experts, and fighters to carry out the attack. Insurgents disperse these networks to prevent

Walls essentially divide networks in half, harming the ability of individual nodes to connect to other nodes in the system. They may run out of material or lose vital experts needed to fight well.

Visually, you can imagine a network Power-law curve. Gated Communities with aggressive policing cuts off the tail ends of the curve, reducing the maximum potential of the hostile network.