You are absolutely right. The union was a much different place then. But.... Everyone, by 1850 understood the ramifications of 'leaving' the union. Nationalism was rising, the state was still a very powerful part of the government, but the USA as a group was becoming a part of peoples lives. Just as the 'sawth' was instantly brotherly after seccesion.
States had fought hard against other states leaving the union. Even when it was the north doing it. I dont think this agreement of the union was as lose as you imagine at this point in america. The north and the republicans were bending over backwards to appease the south at the federal level directly before the war, just to keep the congress happy.
Was the south represented poorly in congress? Did they not have a say in the laws being passed? Were not the states evenly divided at that point between slave and no slave? Yes, but the rich politicians saw that this situation would not continue, no matter what they did. Even the vice president of the confederacy thought it was a bad idea to secede when the democrats controlled congress. They could have done it legally.
Here is a bit about the confederate vp from fordham
Alexander H. Stephens (1812-1883), although originally opposed to secession, was elected vice-president of the Confederacy. After the war he returned to political service in Georgia and in the House of Representatives. He was elected governor of Georgia in 1882 and died in office.
We are in the midst of one of the greatest epochs in our history. The last ninety days will mark one of the most memorable eras in the history of modern civilization.
... we are passing through one of the greatest revolutions in the annals of the world-seven States have, within the last three months, thrown off an old Government and formed a new. This revolution has been signally marked, up to this time, by the fact of its having been accomplished without the loss of a single drop of blood. [Applause.] This new Constitution, or form of government, constitutes the subject to which your attention will be partly invited.
In reference to it, I make this first general remark: It amply secures all our ancient rights, franchises, and privileges. All the great principles of Magna Chartal are retained in it. No citizen is deprived of life, liberty, or property, but by the judgment of his peers, under the laws of the land. The great principle of religious liberty, which was the honor and pride of the old Constitution, is still maintained and secured. All the essentials of the old Constitution, which have endeared it to the hearts of the American people, have been preserved and perpetuated.... So, taking the whole new Constitution, I have no hesitancy in giving it as my judgment, that it is decidedly better than the old. [Applause.] Allow me briefly to allude to some of these improvements. The question of building up class interests, or fostering one branch of industry to the prejudice of another, under the exercise of the revenue power, which gave us so much trouble under the old Constitution, is put at rest forever under the new. We allow the imposition of no duty with a view of giving advantage to one class of persons, in any trade or business, over those of another. All, under our system, stand upon the same broad principles of perfect equality. Honest labor and enterprise are left free and unrestricted in whatever pursuit they may be engaged in ....
But not to be tedious in enumerating the numerous changes for the better, allow me to allude to one other-though last, not least: the new Constitution has put at rest forever all the agitating questions relating to our peculiar institutions-African slavery as it exists among us-the proper status of the negro in our form of civilization. This was the immediate cause of the late rupture and present revolution. Jefferson, in his forecast, had anticipated this, as the "rock upon which the old Union would split." He was right. What was conjecture with him, is now a realized fact. But whether he fully comprehended the great truth upon which that rock stood and stands, may be doubted. The prevailing ideas entertained by him and most of the leading statesmen at the time of the formation of the old Constitution were, that the enslavement of the African was in violation of the laws of nature; that it was wrong in principle, socially, morally and politically. It was an evil they knew not well how to deal with; but the general opinion of the men of that day was, that, somehow or other, in the order of Providence, the institution would be evanescent and pass away. This idea, though not incorporated in the Constitution, was the prevailing idea at the time. The Constitution, it is true, secured every essential guarantee to the institution while it should last, and hence no argument can be justly used against the constitutional guarantees thus secured, because of the common sentiment of the day. Those ideas, however, were fundamentally wrong. They rested upon the assumption of the equality of races. This was an error. It was a sandy foundation, and the idea of a Government built upon it-when the "storm came and the wind blew, it fell."
Our new Government is founded upon exactly the opposite ideas; its foundations are laid, its cornerstone rests, upon the great truth that the negro is not equal to the white man; that slavery, subordination to the superior race, is his natural and moral condition. [Applause.] This, our new Government, is the first, in the history of the world, based upon this great physical, philosophical, and moral truth. This truth has been slow in the process of its development, like all other truths in the various departments of science. It is so even amongst us. Many who hear me, perhaps, can recollect well that this truth was not generally admitted, even within their day. The errors of the past generation still clung to many as late as twenty years ago. Those at the North who still cling to these errors with a zeal above knowledge, we justly denominate fanatics. All fanaticism springs from an aberration of the mind; from a defect in reasoning. It is a species of insanity. One of the most striking characteristics of insanity, in many instances, is, forming correct conclusions from fancied or erroneous premises; so with the anti-slavery fanatics: their conclusions are right if their premises are. They assume that the negro is equal, and hence conclude that he is entitled to equal privileges and rights, with the white man.... I recollect once of having heard a gentleman from one of the Northern States, of great power and ability, announce in the House of Representatives, with imposing effect, that we of the South would be compelled, ultimately, to yield upon this subject of slavery; that it was as impossible to war successfully against a principle in politics, as it was in physics or mechanics. That the principle would ultimately prevail. That we, in maintaining slavery as it exists with us, were warring against a principle-a principle founded in nature, the principle of the equality of man. The reply I made to him was, that upon his own grounds we should succeed, and that he and his associates in their crusade against our institutions would ultimately fail. The truth announced, that it was as impossible to war successfully against a principle in politics as well as in physics and mechanics, I admitted, but told him it was he and those acting with him who were warring against a principle. They were attempting to make things equal which the Creator had made unequal.
In the conflict thus far, success has been on our side, complete throughout the length and breadth of the Confederate States. It is upon this, as I have stated, our social fabric is firmly planted; and I cannot permit myself to doubt the ultimate success of a full recognition of this principle throughout the civilized and enlightened world.
As I have stated, the truth of this principle may be slow in development, as all truths are, and ever have been, in the various branches of science. It was so with the principles announced by Galileo-it was so with Adam Smith and his principles of political economy. It was so with Harvey, and his theory of the circulation of the blood. It is stated that not a single one of the medical profession, living at the time of the announcement of the truths made by him, admitted them. Now, they are universally acknowledged.
