Today is the anniversary of the Gettysburg Address.  In 1987, President Reagan said:

This is Lincoln’s greatest lesson, this lesson in liberty. He understood that the idea of human liberty is bound up in the very nature of our nation. He understood that America cannot be America without standing for the cause of freedom. He had often asked himself, Mr. Lincoln once said, what great principle or idea it was that held the Union together for so long. “It was not,” he said, “the mere matter of the separation … from the motherland.” It was something more. It was “… something in that Declaration of Independence giving liberty, not alone to the people of this country, but hope to the world . . . it was that which gave promise that in due time the weights should be lifted from the shoulders of all men.”