Why should Texas think that? It was a mutual agreement between Texas and the United States. If the agreement was to be ended, it should have required the same mutual consent by both parties.
I found this article from the Washington Post, by James Loewen. It covers much of the same ground that has already been covered in this thread, but it’s a good summary.
The South seceded over states’ rights. (Loewen says “In fact, Confederates opposed states’ rights — that is, the right of Northern states not to support slavery” and supports this with quotes from the South Carolina Declaration of Secession.)
Secession was about tariffs and taxes.
Most white Southerners didn’t own slaves, so they wouldn’t secede for slavery. (But many of them aspired to become slaveowners. And “secession would maintain not only slavery but the prevailing ideology of white supremacy as well.”)
Abraham Lincoln went to war to end slavery. (Loewen quotes from Lincoln’s letter to Horace Greeley that is linked to upthread.)
The South couldn’t have made it long as a slave society. (“impossible to disprove but difficult to accept”)
Because part of the Republican platform was that the western territories would remain free and would not become slave states.
Sure, Lincoln promised that the South could keep its slaves. But then what? Once the western territories became free states, the South would be drastically outnumbered in Washington. The writing was on the wall. Slavery was doomed.
And to top it all off, Lincoln was elected without a single slave state elector. The slave states could see their dominance of the national government was ending. Even if Lincoln took no direct action against slavery, his election threatened the institution of slavery. For slavery to thrive, the national government needed to enforce it everywhere, and Lincoln probably wouldn’t have done that.
In my opinion, there would have been further break-ups.
First, if the Confederate States had seceded and succeeded, it would have been seen as a precedent for other regions. Second, the resulting countries would have been weaker than a united United States and less able to resist secession. Third, once the ball got rolling, there would have been a number of separate countries in North America which would have supported secessions in their rivals.
(I know I’ve written about this stuff at least a couple of times in the past, but what the heck.)
In addition to what Little_Nemo said, the British Empire was still a going concern in North America, and the various British colonies on the continent didn’t begin the process of uniting to form Canada until 1867. If the USA had broken up, perhaps the process of Canadian nation-building would have gone differently; in any event, whether or not it included a semi-autonomous Dominion of Canada, an alternate-timeline British Empire would have been in a much stronger position on this continent, and might well have sought to do a little bit of empire-building at the expense of the upstart (and now divided) American Republics.
France, under the Second French Empire of Napoleon III, had staged a major intervention in Mexico at the same time as the United States was embroiled in its own civil war, culminating in the installation of an Austrian nobleman as Emperor of Mexico as a French client. Emperor Maximilian was never very secure on his new throne, and (not entirely coincidentally) after the United States got its act back together, the French withdrew their support for the Second Mexican Empire, and Emperor Maximilian was overthrown and executed. Oh, and less than 20 years before Napoleon III installed Maximilian on the throne of Mexico, Mexico had lost a war to the United States, and thereby lost about half its national territory. So, you’ve got a brand-new foreign ruler, trying to persuade the Mexicans to accept his reign, and–if the Union loses the American Civil War–the country that had conquered half of Emperor Maximilian’s new country within living memory breaks apart. Hm…Emperor Maximilian (perhaps openly backed by the French Empire) might have been very tempted to take a page from Henry V and see if he could rally the Mexican people to him by starting a nice glorious war for the redemption of the lost northern provinces.
Oh, and France and Britain were not yet allies. In the real world, the two colonial empires had a bit of a war scare (the “Fashoda Incident”) thirty-odd years after the American Civil War, over competing imperial claims in Africa. In an alternate timeline in which the Confederacy wins its independence, Britain and France might have come to blows in North America, or at least done a lot of plotting and scheming against each other, with the American Republics (however many of them there wound up being) as pawns.
The Russian Empire also still had territory in North America–in addition to Canadian Confederation, 1867 was also the year the victorious Union bought Alaska. Spain still ruled Cuba and Puerto Rico; Southern pro-slavery forces had made a play for Cuba a few years before the outbreak of the American Civil War (and of course Spain would go on to lose its last American colonies in a war against the unified USA the same year as the Fashoda Incident). An alternate timeline Russia might not have been as willing to sell Alaska to a weakened USA; an alternate timeline Spain might have been tempted to try to take some steps to secure what remained of its Latin American empire from the expansionist–but now divided–Norteamericanos. Neither Russia nor Spain would likely be a major player in a North American Great Game, but they could have maybe complicated things on the edges.
The point being, the supposed happy re-unification of the United States after a Confederate victory wouldn’t be happening in a vacuum. There were some other parties with interests on this continent who might have been very happy to help things along when it came to the continued disintegration of the American Republics. (Oh, and one or more of the American Republics still has chattel slavery? My goodness, it would just be our Christian duty to intervene in a thing like that…and of course if it meant expanding our Empire a bit, why, all the better!)
I feel Russia and Spain were played out as far as new imperial colonies were concerned. But Germany and Japan were rising powers that were looking for places to establish an colonial empire. If the United States was broken up and unable to enforce the Monroe Doctrine, they would have looked towards Latin America.
The historical USA was not capable of truly enforcing the Monroe doctrine until almost the 20th century, Britain was actually the primary one enforcing it since ‘no further European colonies in America’ suited their goals. The fact that Britain grabbed the Falkland islands and Belize without the US enforcing anything really highlights that. And the post-civil-war US would have to get to work enforcing in immediately, since there was already a major crisis.
In 1862 French forces installed Emperor Maxmillian in Mexico, and only left in 1865 when the now-victorious US moved large, threatening armies to the border of Mexico. I don’t think that a United States that had just lost a war and would not be able to station troops in now-Confederate Texas could pose a credible threat to French forces in Mexico. With such a flagrant and major violation of the Monroe Doctrine going unchecked, I don’t think it would remain a credible factor in foreign policy.