In >hindsight< , the South should have seceded in 1848-1849, right after the Mexican War over issues of tariffs or unbalanced federal expenditures on Northern infrastructure. Centralizing the government was not yet a popular notion in the North (not enough to fight about it) and there was no Kansas/Missouri civil war to complicate matters. And if the so-called border states wanted to wait and see, well--they could wait for Lincoln to get elected and see how they liked being left behind.