Whats the REAL reason marijuanna is illegal in the US for the most part?

I've always been completely free of drugs and alcohol because they just never had an appeal to me like they do to so many others out there but I'm asking this question out of pure curiosity. Is it illegal because drug companies want to push their pain killer meds instead and would go out of business if pot was legalized? Is it illegal to justify states having large police forces?? Is it illegal because of some evil government need/plan to break the power of the middle class so otherwise productive people can be arrested and imprisoned for victimless crimes? Is the reason something else or all of the above??