The balance of power between the sections in the Senate, which had been maintained without difficulty thus far, was seriously threatened by this Missouri question. At the beginning of the Constitutional Union seven States were clearly destined by their climate and occupation for free labour, leaving six for slave labour. The latter thus lacked two senatorial votes of equalling the North from the beginning. The admission of Vermont and Kentucky, a Northern and a Southern State, maintained the ratio. It was continued farther by the admission of Tennessee and Ohio, Louisiana and Indiana, Mississippi and Illinois. This balance had been thus far an accident, depending upon the time when a portion of land had sufficient population for statehood; but it had become such a tacit understanding, that the admission of Alabama in 1819, it was said, made the sections exactly equal in the number of Senators. At almost the same time Missouri and Maine were ready. The latter because of climate must undoubtedly be admitted as a free State. The former must be given to slavery if the balance between the two sections was to be maintained. But the extension of the line of thirty-six thirty would make Missouri a free State. The location of States heretofore admitted had been so indisputably upon the one side or the other of the slavery-freedom line that uncertainty was impossible. Missouri, as has been shown, lay right athwart the extension. There had been comparatively little anti-slavery agitation thus far, being confined to attacks upon the slave trade and an occasional petition from the Friends; yet the sentiment that slavery was an economic evil was firmly established in the overstocked border slave States, and that it was both an economic and moral evil was believed by a growing number in the Northern States. The "Lower South," or Gulf States, were thus left as the guardians of a system which the increasing cultivation of cotton in that region made unusually profitable and, as they thought, indispensable. Missouri lay far to the north of them, but the maintenance of political power in the Union was essential to their future if they read aright the growing hostile sentiment of the North. Immediate or gradual emancipation had been provided by every old State in the North, and slavery had been prohibited by the constitutions of the new Northern States. Feeling the approval of a good conscience, it was probable that the North would eventually demand a kindred movement in the South. There is no reformer likely to be so intolerant as the one who has left off what he considers a bad habit.