If slavery be permitted in Missouri with the climate, and soil, and in the circumstances of this territory, what hope can be entertained that it will ever be prohibited in any of the new States that will be formed in the immense region west of the Mississippi? Will the co-extensive establishment of slavery and of the new States throughout this region, lessen the dangers of domestic insurrection, or of foreign aggression? Will this manner of executing the great trust of admitting new States into the Union, contribute to assimilate our manners and usages, to increase our mutual affection and confidence, and to establish that equality of benefits and burdens which constitutes the true basis of our strength and union? Will the militia of the nation, which must furnish our soldiers and seamen, increase as slaves increase? Will the actual disproportion in the military service of the nation be thereby diminished?--a disproportion that will be, as it has been, readily borne, as between the original States, because it arises out of their compact of Union, but which may become a badge of inferiority, if required for the protection of those who, being free to choose, persist in the establishment of maxims, the inevitable effect of which will deprive them of the power to contribute to the common defence, and even of the ability to protect themselves. There are limits within which our federal system must stop; no one has supposed that it could be indefinitely extended--we are now about to pass our original boundary; if this can be done without affecting the principles of our free governments, it can be accomplished only by the most vigilant attention to plant, cherish, and sustain the principles of liberty in the new States, that may be formed beyond our ancient limits; with our utmost caution in this respect, it may still be justly apprehended that the General Government must be made stronger as we become more extended. But if, instead of freedom, slavery is to prevail and spread, as we extend our dominion, can any reflecting man fail to see the necessity of giving to the General Government greater powers, to enable it to afford the protection that will be demanded of it? powers that will be difficult to control, and which may prove fatal to the public liberties. WILLIAM PINKNEY, OF MARYLAND. (BORN 1764, DIED 1822.) ON THE MISSOURI QUESTION'--UNITED STATES SENATE, FEBRUARY 15, 1820.