This being the case, it is worth noticing that both Lincoln and Douglas confined their disputation closely to the slavery question. Disunion and secession were words familiar in every ear, yet Lincoln referred to these things only twice or thrice, and incidentally, while Douglas ignored them. This fact is fraught with meaning. American writers and American readers have always met upon the tacit understanding that the Union was the chief cause of, and the best justification for, the war. An age may come when historians, treating our history as we treat that of Greece, stirred by no emotion at the sight of the "Stars and Stripes," moved by no patriotism at the name of the United States of America, will seek a deeper philosophy to explain this obstinate, bloody, costly struggle. Such writers may say that a rich, civilized multitude of human beings, possessors of the quarter of a continent, believing it best for their interests to set up an independent government for themselves, fell back upon the right of revolution, though they chose not to call it by that name. Now, even if it be possible to go so far as to say that every nation has always a right to preserve by force, if it can, its own integrity, certainly it cannot be stated as a further truth that no portion of a nation can ever be justified in endeavoring to obtain an independent national existence; no citizen of this country can admit this, but must say that such an endeavor is justifiable or not justifiable according as its cause and basis are right or wrong. Far down, then, at the very bottom lay the question whether the Southerners had a sufficient cause upon which to base a revolution. Now this question was hardly conclusively answered by the perfectly true statement that the North had not interfered with Southern rights. Southerners might admit this, and still believe that their welfare could be best subserved by a government wholly their own. So the very bottom question of all still remained: Was the South endeavoring to establish a government of its own for a justifiable reason and a right purpose? Now the avowed purpose was to establish on an enduring foundation a permanent slave empire; and the declared reason was, that slavery was not safe within the Union. Underneath the question of the Union therefore lay, logically, the question of slavery.