“the human mind… perhaps the most powerful weapon. second only to the "GUN"”

Statement quoted in the Boston Globe (25 October 1977)
Context: Even today, we are still accused of racism. This is a mistake. We know that all interracial groups in South Africa are relationships in which whites are superior, blacks inferior. So as a prelude whites must be made to realize that they are only human, not superior. Same with blacks. They must be made to realize that they are also human, not inferior.

Source: Superman: Red Son

White Racism and Black Consciousness
I Write What I Like (1978)
Variant: The greatest weapon in the hand of the oppressor is the mind of the oppressed.

Howard Gardner, cited in: Richard L. Daft (2014), The Leadership Experience, p. 273

Der Motor des Panzers ist ebenso seine Waffe wie die Kanone.
As quoted in Die Deutschen gepanzerten Truppen bis 1945 (1965) by Oskar Munzel, p. 159

1960s, Where Do We Go from Here: Chaos or Community? (1967)
Context: As long as the mind is enslaved, the body can never be free. Psychological freedom, a firm sense of self-esteem, is the most powerful weapon against the long night of physical slavery. No Lincolnian emancipation proclamation or Johnsonian civil rights bill can totally bring this kind of freedom. The negro will only be free when he reaches down to the inner depths of his own being and signs with the pen and ink of assertive manhood his own emancipation proclamation. And, with a spirit straining toward true self-esteem, the Negro must boldly throw off the manacles of self-abegnation and say to himself and to the world, "I am somebody. I am a person. I am a man with dignity and honor. I have a rich and noble history, however painful and exploited that history has been. Yes, I was a slave through my foreparents, and now I’m not ashamed of that. I'm ashamed of the people who were so sinful to make me a slave." Yes, yes, we must stand up and say, "I'm black, but I'm black and beautiful." This, this self-affirmation is the black man's need, made compelling by the white man's crimes against him.

" Lighting your way to a better future : Speech delivered by Mr N R Mandela at launch of Mindset Network http://db.nelsonmandela.org/speeches/pub_view.asp?pg=item&ItemID=NMS909&txtstr=education%20is%20the%20most%20powerful," July 16, 2003 at db.nelsonmandela.org. ; Cited in: Nelson Mandela, ‎S. K. Hatang, ‎Sahm Venter (2012) Notes to the Future: Words of Wisdom. p. 101.
2000s
Context: Education is the most powerful weapon we can use to change the world and is a powerful part of that world changing arsenal.

Source: Keeping Together in Time (1995), Ch. 4: Religious Ceremonies.