It cannot, however, be contended that there was any obligation, legal or moral, resting upon the Government of the United States toward any of the citizens of the United States, or any of the Commonwealths, to maintain slavery in the province of Louisiana and in the {57} Territories carved out of it. There was, as we have seen, a provision in the Treaty of cession of 1803, by which the United States Government obligated itself to France to protect the property of the inhabitants of the province. But the Government of the United States was under no obligation to any citizen of the United States, or to any Commonwealth of the Union, to keep this Treaty inviolate. It may be affirmed, then, that the United States Government had, in the case of Louisiana, for the first time, permitted and maintained slavery in territory where it was perfectly free to act in regard to this subject as it would, in so far as its own citizens were concerned. This certainly manifested a great increase in the power of the slave-holders over the general Government. [Sidenote: Interest in slavery in Maryland and Virginia increased by the acquisition of Louisiana.] In consequence of this vast territorial extension of slavery the interest of the more Northern of the old slave-holding Commonwealths in slavery was, during this period, greatly re-enlivened. Maryland and Virginia were already, in 1807, overstocked with slaves. The opening up of the virgin lands of the Southwest to the immigration of masters and slaves from the older Commonwealths, and the abolition of the foreign slave-trade, now made the Southwest an excellent market for the surplus slave population of these older Commonwealths. [Sidenote: The domestic slave-trade.] The domestic slave-trade began now to be one of the chief sources of the wealth of Maryland and Virginia especially. Those who participated in this traffic justified it by the claim that it was better for the slaves themselves to be removed to new homes, where they could be better supported, than to be kept in their old homes and suffer for the want of the necessaries of life, and that the distribution of the slave {58} population over a larger area would make future emancipation easier, and less dangerous to the supremacy of the white race. There was a certain force in this reasoning. The mass of the slave-holders seem to have been fully convinced of its soundness, although it did not entirely quiet the consciences of the best men among them to the many painful incidents connected with the separation of the slaves, made subject to this traffic, from their old homes and associations. It is easy to see, however, that the raising of negro slaves, having become a most profitable industry in the older Commonwealths, acted as a vast bribe upon the ideas of men in regard to the questions of the perpetuation and extension of slavery, and beclouded their consciences in respect thereto.