In 1961, President Dwight D. Eisenhower warned us about "the disastrous rise of misplaced power" that our military-industrial complex would spawn, but we can trace the incestuous relationship between the military and private enterprise back to at least the 19th century. Prussian Chief of Staff Helmuth von Moltke (the elder), who used the transportation revolution of his era to transform the Prussian Army and win the German Wars of Reunification, had significant stock holdings in the Prussian railway system.
In 21st century America, we've honed this type of bedfellowing to a fine art. You can't count the hands of everybody who is knocking off a piece of the defense dollar because everybody's hands are in somebody else's pockets. Generals involved in system and doctrine development during their active duty careers retire and go to work for the companies who are developing the very same systems and doctrines. The colonels, majors, and sergeant majors who used to work for the generals retire as well and go back to work for their old bosses on the outside. The retired guys work hand-in-purse on project development with their still on active duty counterparts who are, themselves, looking to retire soon and go back to work doing the same thing they've been doing.
The retired guys take their pet projects to their active duty buddies who insert them into so-called "battle experiments" then rig the games to ensure said pet projects emerge victorious. Everyone publishes after-action reports that hail the projects as having passed "objective" and "empirical" scrutiny. Contracts are drawn up, production lines open, and the military-industrial caisson goes rolling along.
In 19th century Prussia, they called this sort of thing "die Korruption." In 21st century America we call it "business as usual."
The military-industrial complex has achieved what Ike described as "unwarranted influence" over "the councils of government." Regional economies and political careers are wholly dependent on it, as are the empirical aims of "war hawk" leaders. Few are naïve enough to believe that the U.S. can survive and thrive without a credible, capable defense establishment. But America today looks entirely too much like 19th century Prussia--a country that's a life support system for its military.