Daniel Ellsberg, a high U.S. official, who felt indignant at the reality of the Vietnam war, decided to illegally send the documents in his hands to the press. On June 13, 1971, the U.S. East coast reference daily, the New-York Times, started the publication of those Pentagon Papers: 7000 pages of classified defense secrets.
Those revelations had the effect of a bomb. Far from what was presented by the official propaganda, they brought out the disastrous political handling of the war as well as countless atrocities. President Richard Nixon and his administration vainly tried to ban the publication in the name of national security.
Daniel Ellsberg would pay dearly for his public-spiritedness, but gave the U.S. democracy new encouragement, making people become rapidly aware of their opinion and the U.S. retreat from Vietnam.