Please explain how the secession of South Carolina was an attempt at the "militant radical spread of slavery".
Looks to me like SC was trying to avoid federal interference and was protesting violations of the constitution. There is nothing in the secession of SC that had anything to do with spreading slavery.
But what was the Constitutional violation in the election of Abraham Lincoln? The secessionists might not have liked higher tariffs, but as long as they were Constitutionally enacted, what is the complaint? And I have no doubt that Northern and Southern Democrats acting in concert could have modified that.
What kind of federal interference are you talking about, and what Constitutional violations were they protesting?