“The history of human conduct does not warrant that exalted opinion of human virtue which would make it wise in a nation to commit interests of so delicate and momentous a kind as those which concern its intercourse with the rest of the world to the sole disposal of a magistrate, created and circumstanced, as would be a President of the United States.”

in Indonesia, Palestine, and Kashmir - has demonstrated convincingly that parties to the most severe conflict may be induced to abandon war as the method of settlement in favour of mediation and conciliation, at a merciful saving of untold lives and acute suffering. Unfortunately, there may yet be some in the world who have not learned that today war can settle nothing, that aggressive force can never be enough, nor will it be tolerated. If this should be so, the pitiless wrath of the organized world must fall upon those who would endanger the peace for selfish ends. For in this advanced day, there is no excuse, no justification, for nations resorting to force except to repel armed attack.
Some Reflections on Peace in Our Time (1950)

To Jinping Xi (2011-2012), as quoted in "Born Red: How Xi Jinping, an unremarkable provincial administrator, became China’s most authoritarian leader since Mao." http://www.newyorker.com/magazine/2015/04/06/born-red (6 April 2015), by Evan Osnos, The New Yorker.
2010s

1790s, Farewell Address (1796)

1930s, Quarantine Speech (1937)

§ 5
From Lives and Opinions of the Eminent Philosophers by Diogenes Laërtius

Source: Man's Search for Meaning

Science and the Unseen World (1929)
Context: The scientific answer is relevant so far as concerns the sense-impressions... For the rest the human spirit must turn to the unseen world to which it itself belongs.<!--IV, p.43

Day of Affirmation Address (1966)

1963