If matters had remained as they were, there is little room for doubt that the settlement reached in the Missouri Compromise would have endured for another generation at the least. It is true that, once raised, the issue between free labor and slavery was, as Mr. Seward afterwards said, "an irrepressible conflict." It is morally certain that sooner or later, in one way or in another, it was bound to lead to a decisive struggle either of war or of diplomacy between the North and the South. But we are dealing now with facts and not with probabilities; with events and not with conjectures; and the facts and events strongly suggest that if no new condition had intervened to disturb the settlement made by the Missouri Compromise, that adjustment of the vexed and vexing slavery question would have endured for at least a generation longer than in fact it did.
The new circumstance that intervened was the annexation of Texas. Texas was a vast territory, undefined as to its limits at that time, but covering an area eight or ten times greater than that of the largest state then in the Union. It included the present state of Texas, New Mexico, and a large area besides. It had been a part of Mexico, peopled chiefly by emigrants from the United States under whose inspiration it had revolted and achieved its independence as a republic.
Its desire for annexation to the Union was quite natural and inevitable and but for slavery that desire would have been reciprocated throughout the United States. It was easily foreseen, however, that the annexation of this vast territory, lying as it did south of the line that set the limit to slavery, would open to that institution an opportunity of expansion scarcely less than that opened to free labor by the Missouri Compromise.
The policy of annexation was bitterly opposed on this ground and additionally because of the practical certainty that annexation would involve a war with Mexico.
Years before that time, Henry Clay had severely criticized the administration for having failed to insist upon our right to Texas as a part of the Louisiana Purchase, but now, in his anxiety to keep the slavery question out of politics because of the danger it involved to the Union, he was strongly opposed to the annexation policy.