Brazil was a monarchy in the 1880s. Protests against the abolition of slavery were an important factor in the overthrow of the monarchy. Most countries in our hemisphere either had few slaves and slaveowners or they were governed from abroad. Countries that had a large population of slaveowners and no colonial overlord were few, and in such countries the abolition of slavery was likely to lead to war. That was the case in the US. In Brazil it cost an emperor his throne. In the first country in the hemisphere to abolish slavery, it took a bloody revolution and war.
Clearly, no one can imagine slavery continuing in North America down to the 21st century. It would have been abolished eventually. But some people are too complacent and smug about emancipation happening "eventually." Imagine taking that kind of attitude to any other evil, doing nothing and simply saying eventually it would pass. And this at a time -- the 1860s -- when many political leaders were quite enthusiastic about slavery and its expansion.
-- The South would have had to put up a wall to keep people in.
That's an exaggeration. You underestimate both what the Southern states were willing to do to stop runaways and what Southerners actually did do. If you were used to being called out to hunt down runaways, you wouldn't have any problem putting in efforts to secure the border. A haven in Canada didn't lead to an end of slavery, nor would a break-up of the US necessarily have done so.
-- Slavery wasn't the primary cause of the War; just one of many. Taxation (specifically the Morrill Tariff) was also a major cause.
Whatever else was involved, slavery was the primary cause of the war. Without slavery, the two sections wouldn't have grown so hostile to each other, and without the perceived threat to slavery and its expansion, there would have been no secession in 1860.
-- The Confederates DID NOT believe they were creating a true nation; they believed they were restoring the True United States (believing the Union had left its principles)
The idea that the Union had betrayed its principles was tied to the defense of "Southern right," which largely meant the rights of slaveowners. Surely you've heard of Southern nationalism. In fact, it turned out not to be such a strong force among the people. We weren't two countries, and there hasn't been much prosecessionist sentiment since 1865.
Prior to the Civil War, though, there were plenty of passionate promoters of the idea that we were two different peoples. Such nationalists were an important force in bringing about secession and the formation of the Confederacy. You might take a look at DeBow, Toombs, Wigfall, Ruffin, Rhett, Keitt, Yancey, and other extremist "fire-eaters" who were determined to get an independent Southern nation for themselves. A Confederate government, like any other government, would do what it could to maintain its power, not to dissolve it. And if they'd won the war or been given their independence, that's what they'd do.
-- I apply the "eventually" argument to the War Between the States because of the damage it did. Beyond the massive loss of life, it DESTROYED the Old Republic and issued in an era of Big Government.
So far as I can see, nothing you've said has had very much substance in it beyond the fact that the war was quite bloody and destructive. The Civil War didn't destroy the "Old Republic." Secession did that. Whatever came afterwards would be different. Nor did the war bring along an era of Big Government. That happened in the 20th century. Nor was Lincoln's idea of union so very different from George Washington's or James Madison's or Andrew Jackson's.
Do you believe that states have a right to secede?
No Big Government? Here's Lincoln's New Deal:
- Morrill Tariff (1861)
- First Income Tax (1861)
- Expanded Postal Service (1861)
- Homestead Act (1862)
- Morrill Land-Grant College Act (1862)
- Department of Agriculture (1862)
- Bureau of Printing and Engraving (1862)
- Transcontinental Railroad Land Grants (1862, 1863, 1864)
- National Banking Acts (1863, 1864, 1865, 1866)
- Comptroller of the Currency (1863)
- National Academy of Science (1863)
- Free urban mail delivery (1863)
- Yosemite public nature reserve land grant (1864)
- Contract Labor Act (1864)
- Office of Immigration (1864)
- Railway mail service (1864)
- Money order system (1864)