One of the (possibly) profound effects of psychedelic experiences is the dissolution of boundaries-- a heightening of the dissociative pattern matching behavior that we call human cognition to the point that everything seems relevant to everything and nothing is really different from anything else.

To an extent this is trivially true, and it certainly inspires a lot of not-too-insightful discussion about how we're all stars, man, but it can also point out the important but non-obvious fact that your neighbor is a person just like you are, having exactly the same experience of consciousness that you are, and so is the President, and so is that bum on the street, and so is that person in the country across the river that you're supposed to hate. She's just like you, and you can't hate yourself. So it shouldn't be surprising (for this reason among others) that people who smoke a lot of weed find the idea of war to be a waste of time when, really, we could all just be relaxing with some good friends, music and food.

Is it really that hard to imagine that this idea, whether brought on by drugs, education, or meditation, is threatening to the few in power who use these artificial divisions to control the many?

Obviously not, but the original Controlled Substances Act, the beginning of our modern War on Drugs, can be reasonably inferred as direct response to the anti-war movement.

That Act is only in effect in the US, though, while drugs are forbidden in many countries.

That doesn't mean it wasn't a contributing factor. Also, the US foreign policy has exported our nation's legislative opinion of drugs for decades.