Red Dawn, discussed on this site as Guerilla War classic. Movie is much deeper than one would suspect from Patrick Swayze, though Roadhouse was Tao. Hard to pick one scene.

The Quiet American. Graham Greene's novel of an American trying to help "the locals" with the best of intentions, though his methods are suspect and dangerous. Michael Caine, playing the expatriate reporter, realizes Brendan Frazier, Aid worker's true identity.

Breaker Morant. What is ethical, who is a combatant, what is justice in war?
Australian Soldiers are tried for murdering a priest accused of aiding the Bo'ers in South Africa. Again, hard to pick just one scene. maybe the "confession" by the Australians, talking about what really happened.