“Great ideas do not burst upon the world unannounced. They are reached by a gradual development over a length of time usually proportionate to their importance. This is especially true of the principles laid down in the Declaration of Independence. Three very definite propositions were set out in its preamble regarding the nature of mankind and therefore of government. These were the doctrine that all men are created equal, that they are endowed with certain inalienable rights, and that therefore the source of the just powers of government must be derived from the consent of the governed. If no one is to be accounted as born into a superior station, if there is to be no ruling class, and if all possess rights which can neither be bartered away nor taken from them by any earthly power, it follows as a matter of course that the practical authority of the Government has to rest on the consent of the governed. While these principles were not altogether new in political action, and were very far from new in political speculation, they had never been assembled before and declared in such a combination.”

1920s, Speech on the Anniversary of the Declaration of Independence (1926)
Context: If all men are created equal, that is final. If they are endowed with inalienable rights, that is final. If governments derive their just powers from the consent of the governed, that is final. No advance, no progress can be made beyond these propositions. If anyone wishes to deny their truth or their soundness, the only direction in which he can proceed historically is not forward, but backward toward the time when there was no equality, no rights of the individual, no rule of the people. Those who wish to proceed in that direction can not lay claim to progress. They are reactionary. Their ideas are not more modern, but more ancient, than those of the Revolutionary fathers.

Those are undeniable truths.
Vietnamese Proclamation of Independence (2 September 1945), Ho Chi Minh, Selected Works (1960-1962), Vol. 3, pp. 17-21

1920s, Equal Rights (1920)
Context: July 4, 1776 was the historic day on which the representatives of three millions of people vocalized Concord, and Lexington, and Bunker Hill, which gave notice to the world that they proposed to establish an independent nation on the theory that all men are created equal, that they are endowed by their creator with certain inalienable rights, that among these are life, liberty, and the pursuit of happiness. The wonder and glory of the American people is not the ringing Declaration of that day, but the action then already begun, and in the process of being carried out, in spite of every obstacle that war could interpose, making the theory of freedom and equality a reality.

This they said, and this meant. They did not mean to assert the obvious untruth, that all were then actually enjoying that equality, nor yet, that they were about to confer it immediately upon them. In fact they had no power to confer such a boon. They meant simply to declare the right, so that the enforcement of it might follow as fast as circumstances should permit. They meant to set up a standard maxim for free society, which should be familiar to all, and revered by all; constantly looked to, constantly labored for, and even though never perfectly attained, constantly approximated, and thereby constantly spreading and deepening its influence, and augmenting the happiness and value of life to all people of all colors everywhere. The assertion that "all men are created equal" was of no practical use in effecting our separation from Great Britain; and it was placed in the Declaration, nor for that, but for future use. Its authors meant it to be, thank God, it is now proving itself, a stumbling block to those who in after times might seek to turn a free people back into the hateful paths of despotism. They knew the proneness of prosperity to breed tyrants, and they meant when such should re-appear in this fair land and commence their vocation they should find left for them at least one hard nut to crack. I have now briefly expressed my view of the meaning and objects of that part of the Declaration of Independence which declares that "all men are created equal".
1850s, Speech on the Dred Scott Decision (1857)

Obergefell v. Hodges http://www.supremecourt.gov/opinions/14pdf/14-556_3204.pdf (26 June 2015), pp. 16-17.
2010s

1850s, The Present Aspect of the Slavery Question (1859)
Context: Such is the present aspect of the slavery question. For myself, I believe that the faith in which the government was founded still survives. I believe that the spirit of despotism which now says to the country, 'I will rule or ruin', will hear the imperial voice of the conscience of the American people, recognizing that justice and prosperity walk hand in hand, saying, 'You will do neither'. I believe that God did not hide this continent through all time as the spot whereon a nation should be planted upon the only principle that can render a nation as permanent as the race, to suffer the experiment to fail within a century. I believe these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain inalienable rights, that among these are life, liberty, and the pursuit of happiness. Do you believe it? If aye, let us go into the battle, and God speed the right.

That is the true genius of America—a faith in simple dreams, an insistence on small miracles.
2004, Democratic National Convention speech (July 2004)

As quoted in letter to the citizens of the twelfth congressional district (29 June 1839), The Hingham Patriot, MA. As quoted in Thomas Huges Rare and Early Newspaper catalog, No. 141
Letter to the 12th Congressional District (1839)

1850s, Speech on the Dred Scott Decision (1857)
Context: I think the authors of that notable instrument intended to include all men, but they did not intend to declare all men equal in all respects. They did not mean to say all were equal in color, size, intellect, moral developments, or social capacity. They defined with tolerable distinctness, in what respects they did consider all men created equal; equal in "certain inalienable rights, among which are life, liberty, and the pursuit of happiness." This they said, and this meant. They did not mean to assert the obvious untruth, that all were then actually enjoying that equality, nor yet, that they were about to confer it immediately upon them. In fact they had no power to confer such a boon. They meant simply to declare the right, so that the enforcement of it might follow as fast as circumstances should permit. They meant to set up a standard maxim for free society, which should be familiar to all, and revered by all; constantly looked to, constantly labored for, and even though never perfectly attained, constantly approximated, and thereby constantly spreading and deepening its influence, and augmenting the happiness and value of life to all people of all colors everywhere. The assertion that "all men are created equal" was of no practical use in effecting our separation from Great Britain; and it was placed in the Declaration, nor for that, but for future use. Its authors meant it to be, thank God, it is now proving itself, a stumbling block to those who in after times might seek to turn a free people back into the hateful paths of despotism. They knew the proneness of prosperity to breed tyrants, and they meant when such should re-appear in this fair land and commence their vocation they should find left for them at least one hard nut to crack. I have now briefly expressed my view of the meaning and objects of that part of the Declaration of Independence which declares that "all men are created equal".