but positive protection at the hands of a population whose institutions were naturally antagonistic to the slave idea.  This being the case, she must be alarmed at seeing that population steadily outstripping her own in numbers and wealth.[61] Since she could not possibly even hold this disproportion stationary, her best resource seemed to be to endeavor to keep it practically harmless by maintaining a balance of power in the government.  Thus it became unwritten law that slave States and free States must be equal in number, so that the South could not be outvoted in the Senate.  This system was practicable for a while, yet not a very long while; for the North was filling up that great northwestern region, which was eternally dedicated to freedom, and full-grown communities could not forever be kept outside the pale of statehood.  On the other hand, apart from any question of numbers, the South could make no counter-expansion, because she lay against a foreign country.  After a time, however, Texas opportunely rebelled against Mexico, and then the opportunity for removing this obstruction was too obvious and too tempting to be lost.  A brief period of so-called independence on the part of Texas was followed by the annexation of her territory to the United States,[62] with the proviso that from her great area might in the future be cut off still four other States.  Slavery had been abolished in all Mexican territory, and Texas had been properly a “free” country; but in becoming a part of the United States she became also a slave State.

Mexico had declared that annexation of Texas would constitute a casus belli, yet she was wisely laggard in beginning vindictive hostilities against a power which could so easily whip her, and she probably never would have done so had the United States rested content with an honest boundary line.  But this President Polk would not do, and by theft and falsehood he at last fairly drove the Mexicans into a war, in which they were so excessively beaten that the administration found itself able to gather more plunder than it had expected.  By the treaty of peace the United States not only extended unjustly the southwestern boundary of Texas, but also got New Mexico and California.  To forward this result, Polk had asked the House to place $2,000,000 at his disposal.  Thereupon, as an amendment to the bill granting this sum, Wilmot introduced his famous proviso, prohibiting slavery in any part of the territory to be acquired.  Repeatedly and in various shapes was the substance of this proviso voted upon, but always it was voted down.  Though New Mexico had come out from under the rule of despised Mexico as “free” country, a contrary destiny was marked out for it in its American character.  A plausible suggestion was made to extend the sacred line of the Missouri Compromise westward to the Pacific Ocean; and very little of the new country lay north of that line.  By all these transactions the South seemed to be scoring many telling