First: one key point to remember is that in early 1861 there was no war over secession, slavery, states' rights, tariffs, Confederacy or anything else.
For several months secession & Confederacy proceeded relatively peacefully.
War only began in April 1861 when after months of demanding Fort Sumter's surrender, Jefferson Davis ordered a military assault to force it.
So, did Davis order the assault because of slavery, or tariffs?
No, it was because Davis & other Confederates believed Union troops in Fort Sumter "assailed" their "integrity".
Those are Davis' words from his February 1861 inaugural, in which he promised to start war if that happened.
So Lincoln called up 75,000 troops, over slavery or tariff's or even states' rights?
No, to put down an obvious rebellion, insurrection, domestic violence, invasion and soon even treason, all as authorized in the US Constitution.
Slavery was not then the issue but soon became it when thousands of slaves began escaping to Union Army lines, and what were they going to do?
Well, turns out "contraband of war" was recognized in US law and slaves declared "contraband" could then be freed and hired to support the Union Army effort -- some even as soldiers.
Sure, pro-Confederate mantra is "War of Northern Aggression", but in early 1861 Confederates did all the aggressing, not just in the Deep South but also in Union states like Missouri, Maryland & western Virginia.
By war's end Confederates had military forces invade or operating in 14 of 30 remaining Union states & territories.
So it began & continued as a "War of Confederate Aggression".
Second: slavery ended as a lawful institution nationally on December 18, 1865 with ratification of the 13th amendment.
Before that each state had its own peculiar laws or emancipation enforced by Union Army.
To say, "the South ended slavery before the North" is cockamamie unless by "South" you mean Union enforced emancipation and by "North" you mean such slave-states as Delaware, which waited until the 13th amendment went into force.
a) the Articles of Confederation were articles of perpetual union;
b) the states did not ratify the Constitution of 1789-- it was approved by electors chosen by the people of each state. The state governments simply agreed to abide by the ratification process and accept the new, national government the ratification process created.
So I think there is a reasonable argument to be made that there was no states' right to secede.
That said, it is also clear that the Republican Party platform, which embraced abolition, embraced an end for which there was no Constitutional means.
The only way the Federal government could end slavery would have been through abusive means (such as a tariff on cotton exports) intended to bankrupt the plantation system or through the outright usurpation of unconstitutional powers.
Given Lincoln's election, the South had quite legitimate fears about such a process of usurpation.
Lee's actions are quite instructive in this regard, insofar as he remained an officer of the USA and strongly counseled against secession until it became clear that Virginia would secede and Lincoln would use force to maintain the Union.
The war that followed was a tragedy precisely because in many (if different) respects, both sides were right.