“There is one compromise and one only, and that is the United Nations. If the United States and Britain go to the United Nations and the United Nations says we have concrete evidence of the existence of these weapons of mass destruction in Iraq and we feel that we must do something about it, we would all support it. … There is no doubt that the United States now feels that they are the only superpower in the world and they can do what they like. And of course we must consider the men and the women around the president. Gen. Colin Powell commanded the United States army in peacetime and in wartime during the Gulf war. He knows the disastrous effect of international tension and war, when innocent people are going to die, young men are going to die. He knows and he showed this after September 11 last year. He went around briefing the allies of the United States of America and asking for their support for the war in Afghanistan. Dick Cheney, Rumsfeld, they are people who are unfortunately misleading the president. Because my impression of the president is that this is a man with whom you can do business. But it is the men who around him who are dinosaurs, who do not want him to belong to the modern age.”

Barack Obama: "The President's News Conference With President Abdullah Gul of Turkey in Ankara, Turkey," April 6, 2009. Online by Gerhard Peters and John T. Woolley, The American Presidency Project. http://www.presidency.ucsb.edu/ws/index.php?pid=85974&st=&st1=
2009

Attributed to Washington in "Farewell to the United States of Europe: long live the EU!" by André Fontaine at Open Democracy (29 November 2001) http://www.opendemocracy.net/democracy-europefuture/article_344.jsp. It appears to have originally circulated in French:
:: Je suis citoyen de la Grande République de l'Humanité. Je vois le genre humain uni comme une grande famille par des liens fraternels. Nous avons jeté une semence de liberté et d'union qui germera peu à peu dans toute la Terre. Un jour, sur le modèle des Etats-Unis d'Amérique, se constitueront les États-Unis d'Europe. Les États-Unis seront le législateur de toutes les nationalités.
: An anonymous blogger in "Did George Washington predict a "United States of Europe"? (30 January 2010) http://racehist.blogspot.com/2010/01/did-george-washington-predict-united.html showed that it derived from Gustave Rodrigues, Le peuple de l'action: essai sur l'idéalisme américain (A. Colin, 1917), p. 207:
:: Washington écrivait à La Fayette qu'il se condérait comme « citoyen de la grande république de l'humanité » et ajoutait : « Je vois le genre humain uni comme une grande famille par des liens fraternels ». Ailleurs il écrivait, prophétiquement: « Nous avons jeté une semence de liberté et d'union qui germera peu à peu dans toute la terre. Un jour, sur le modèle des Etats-Unis d'Amérique, se constitueront les États-Unis d'Europe. »
: A translation by Louise Seymour Houghton ( The People of Action: An Essay on American Idealism (1918) http://books.google.com/books?id=b8Y9AAAAYAAJ) reads:
:: Washington wrote to Lafayette that he considered himself a "citizen of the great republic of humanity," adding: "I see the human race a great family, united by fraternal bonds." Elsewhere he wrote prophetically: "We have sown a seed of liberty and union that will gradually germinate throughout the earth. Some day, on the model of the United States of America, will be constituted the United States of Europe." [pp. 209-210]
: The first two quotations come from a letter to the Marquis de Lafayette of 15 August 1786 (see above) as quoted in Joseph Fabre's Washington, libérateur de l'Amérique: suivi de Washington et la revolution Américaine (Ch. Delagrave, 1886), and the third is also found in that source where, although placed between quotation marks, it is clearly intended as the author's own comments on what "Washington and his friends" were saying to the world by establishing the American Constitution. Gustave Rodrigues mistakenly printed Fabre's words as Washington's alongside some actual observations of his from a letter to Lafayette, and so created the misquotation.
Misattributed

As quoted in "The Watchman" in TIME magazine (16 August 1948) http://www.time.com/time/magazine/article/0,9171,798932-2,00.html

2000s, 2008, Address to the United Nations General Assembly (September 2008)

http://www.msnbc.msn.com/id/18094428/page/2/

Source: Prozac Nation

On the Irrepressible Conflict (1858)
Context: The Union is a confederation of States. But in another aspect the United States constitute only one nation. Increase of population, which is filling the States out to their very borders, together with a new and extended network of railroads and other avenues, and an internal commerce which daily becomes more intimate, is rapidly bringing the States into a higher and more perfect social unity or consolidation. Thus, these antagonistic systems are continually coming into closer contact, and collision results.
Shall I tell you what this collision means? They who think that it is accidental, unnecessary, the work of interested or fanatical agitators, and therefore ephemeral, mistake the case altogether. It is an irrepressible conflict between opposing and enduring forces, and it means that the United States must and will, sooner or later, become either entirely a slaveholding nation, or entirely a free-labor nation.

The Queen urging nations to work together at her second address of the United Nations http://news.bbc.co.uk/1/hi/uk/10533451.stm

Speech on the Assassination of Martin Luther King, Jr. (1968)