The two great parties on the eve of the Mexican war were thus somewhat similarly situated. In the South all the members of both were, by the supposed necessity of their situation, upholders of slavery, though the Democrats were on this question more aggressive, more truculent, and more menacing, than the Whigs. The Southern Whigs, under the lead of Mr. Clay, had been taught that slavery was an evil, to be removed in some practicable way at some distant period, but not to be interfered with, in the States where it existed, by outside influence or force. The Democrats, under the head of Mr. Calhoun, defended the institution of slavery as right in itself, as scripturally authorized, as essential in the economy of labor, and as a blessing to both races. In the North both parties were divided on the question; each had its anti-slavery wing and its pro-slavery wing, with many local names to distinguish them. Between the two a relentless controversy began,--a controversy marked as much by epithet as by argument, and conducted with such exasperation of feeling as clearly foreshadowed a break of existing party lines, and the formation of new associations, through which, in the phrase of that day, "men who thought alike could act together." THE ACQUISITION OF TERRITORY. This being the condition of the two great parties which divided the country, it was evident that the acquisition of territory from Mexico must lead to an agitation of the slavery question, of which no man could measure the extent, or foresee the consequences. It was the old Missouri struggle renewed, with more numerous combatants, a stronger influence of the press, a mightier enginery of public opinion. It arose as suddenly as the agitation of 1820, but gave indications of deeper feeling and more prolonged controversy. The able and ambitious men who had come into power at the South were wielding the whole force of the national administration, and they wielded it with commanding ability and unflinching energy. The Free-soil sentiment which so largely pervaded the ranks of the Northern Democracy had no representative in the cabinet, and a man of pronounced anti-slavery views was as severely proscribed in Washington as a Roundhead was in London after the coronation of Charles II.