The several States of the Union are by force of the Constitution coequal in domestic legislative power. Congress can not change a law of domestic relation in the State of Maine; no more can it in the State of Missouri. Any statute which proposes to do this is a mere nullity; it takes away no right, it confers none. If it remains on the statute book unrepealed, it remains there only as a monument of error and a beacon of warning to the legislator and the statesman. To repeal it will be only to remove imperfection from the statutes, without affecting, either in the sense of permission, or of prohibition, the action of the States or of their citizens. Still, when the nominal restriction of this nature, already a dead letter in law, was in terms repealed by the last Congress, in a clause of the act organizing the Territories of Kansas and Nebraska, that repeal was made the occasion of a widespread and dangerous agitation. It was alleged that the original enactment being a compact of perpetual moral obligation, its repeal constituted an odious breach of faith. An act of Congress, while it remains unrepealed, more especially if it be constitutionally valid in the judgment of those public functionaries whose duty it is to pronounce on that point, is undoubtedly binding on the conscience of each good citizen of the Republic. But in what sense can it be asserted that the enactment in question was invested with perpetuity and entitled to the respect of a solemn Compact? Between whom was the compact? No distinct contending powers of the Government, no separate sections of the Union treating as such, entered into treaty stipulations on the subject. It was a mere clause of an act of Congress, and, like any other controverted matter of legislation, received its final shape and was passed by compromise of the conflicting opinions or sentiments of the members of Congress. But if it had moral authority over men's consciences, to whom did this authority attach? Not to those of the North, who had repeatedly refused to confirm it by extension and who had zealously striven to establish other and incompatible regulations upon the subject. And if, as it thus appears, the supposed compact had no obligatory force as to the North, of course it could not have had any as to the South, for all such compacts must be mutual and of reciprocal obligation. It has not unfrequently happened that lawgivers, with undue estimation of the value of the law they give or in the view of imparting to it peculiar strength, make it perpetual in terms; but they can not thus bind the conscience, the judgment, and the will of those who may succeed them, invested with similar responsibilities and clothed with equal authority. More careful investigation may prove the law to be unsound in principle. Experience may show it to be imperfect in detail and impracticable in execution. And then both reason and right combine not merely to justify but to require its repeal.