In political science, the "iron triangle" is used to model the relationship between industry, bureaucracy, and the legislature. The classic example of an iron triangle is the military-industrial complex in the USA:
     Defense contractors
            / \
          /     \
        /         \
      /             \
    /                 \
In this case, one corner of the triangle represents the Armed Services Committees in Congress, which appropriate funds for the Department of Defense. DoD, at the second corner, makes decisions about which systems to procure and how they will be deployed. The contractors, like LockMart and Boeing, develop the systems with Congress's money.

These form an iron triangle because they lobby each other vigorously for mutual help. Defense contractors want to make weapons. The Pentagon wants weapons, and wants money from Congress to buy those weapons. Congresspeople want production and deployment to boost the economy in their home constituencies.

The military is not the only example of an iron triangle: any industry paralleled by a bureaucratic organ exhibits a similar lobbying cycle. Many analysts call the oil industry and the Department of Energy part of a strong iron triangle: a similar case could be made for airlines and the FAA, or even labor unions and the Department of Labor.

In the Korean War, the Iron Triangle was formed by the towns of Pyongyang (not that Pyongyang), Chorwon, and Kumhwa, which formed a triangle around a valley chokepoint near Panmunjom. It was the site of heavy trench warfare between United Nations troops and North Korea from 1951 onward.

And then there was the infamous Iron Triangle of the Vietnam War. It was a sixty square mile area, twenty miles north of Saigon, where the Viet Cong had kept underground bases for years.

After evacuating all the civilians they could, United States forces opened free fire on the Iron Triangle in Operation Cedar Falls of January, 1967. It was the first corps-level operation of the war, and it led to the killing of some 1,300 Viet Cong and sympathizers within the Triangle, as well as the destruction of the entire village of Ben Suc.