From the reading to my understanding of it all, the iron triangle is congress, bureaucracy and the interest groups and the three of them are the policy makers. The relationship with congress, military bureaucracies and defense industries is that they are the group that profits from wars.
In 1961 Eisenhower warned our country in his Farwell speech that, “A scientific-technological elite” that would dominate public policy, and of a “ military-industrial complex” that would claim : out toil, resources and livelihood”. Exactly