The "Combine" is what Chief Bromden calls society, which he sees as a massive, oppressive entity that strings individuals together and shunts those members of society that are viewed as "mistakes" to the mental hospital to be locked away. Note how he talks about the Combine in the following quote:
The ward is a factory for the Combine. It's for fixing up mistakes made in the neighbourhoods and in the schools and in the churches, the hospital is. When a completed product goes back out into society, all fixed up good as new, better than new sometimes, it brings joy to the Big Nurse's heart; something that came in all twisted different is now a functioning component, a credit to the whole outfit and a marvel to behold.
Note the mechanistic metaphor that is used throughout this quote. Bromden talks of humans and society as if they are all a machine, with the Combine representing society at large. The hospital becomes a "factory" where humans who are "twisted different" are formed once again into "functioning components," cogs in a machine that will work. Such mechanistic imagery shows how Bromden and the other patients are profoundly dehumanised through their treatment. As parts of a machine, they are not allowed to have their own humanity.