It seems to me that the states who seceded from the Union in the first wave from 1860 and 1861 did so in the belief that the problems they faced in the Union could be better solved from outside of it. However, I do not think that was a very wise idea and I think that they should have known better at the time.
First, while the South was outnumbered in the House of Representatives (although they still had a large minority) and in the White House with Lincoln’s victory, they still had control of the Senate through a Democratic majority. The Federal government, while favoring Republican rule was significantly restrained by the Democratic Party’s influence. When statistics are put together showing how the South was out-manned by a 4-to-1 ratio of military aged males available for military duty, and how the North had exponentially greater manufacturing capacity than the South, it seems strange to me that the leaders of the South chose the greater odds of the battlefield to those of the national legislature.
Second, had the South not seceded but fought its battles on the floors of Congress, the Republican Party was likely to be restrained by law and custom which the Democrats could bring against them and in the courts if need be. Laws, congressional rules, and the balancing power of the judiciary would keep the Republican Party from running a completely unilateral system of power. Contrast this with the decision to secede and then the decision to fire on Fort Sumter. With all of those Democrat Senators and Representatives gone from the Congress due to secession and with war now the only way forward, there was literally no legal restraints on Republican activities.
The South would later decry the illegal nature of the Northern actions just before, during, and after the war but what legal recourse did they have after they seceded? They took the debate about which they had long argued within the confines of law to an arena outside of the confines of law where might alone makes right. If they thought the North was likely to behave in a tyrannical way while under law, how did they think the North would act when law was officially set aside?
In short, by seceding and moving for war, the South cast aside the restraint of law which would have hampered their enemy had they stayed in the Union while simultaneously selecting the method of political contest that gave them the worst odds of all their options. They would have done far more to restrain and resist Lincoln and the Republicans from within the system than by exiting it. And they would have suffered far less damage to their people and economy from within the system as well. Hindsight is 20/20 but I really think that this should have been obvious to all of the leaders of that time.