By no means. The "root cause" of a war can lie very deep indeed. "Root causes" are distinguished from surface causes. Historians who speak of slavery as a "root cause" of the war are trying to explain how it was that the US became divided into two hostile camps, rather than the specific circumstances that sparked the war.
Slaves were chattel property, same status as cattle or livestock and thusly the institution was considered "covered" by Constitutional guarantees of private property ownership.
There were abolitionists who argued that the Constitution and laws actually forbade slavery. That was to be sure very much a minority point of view.
The anarchist Lysander Spooner, beloved by neo-confederates for his attacks on Lincoln, wrote a book on the subject. It's a curiousity, since Spooner didn't believe that the Constitution was a binding authority, but if one values Spooner's contributions, his view on this should also be considered.
The larger point is that there wasn't one unified 19th century opinion on race and slavery. Even if there were it wouldn't be immune from criticism. If you criticize present day thinking about this or that issue, there's no reason why one can't do the same for past positions on social or political questions.
People at the time understood that, and that helps to explain why slaveowners were so terrified of the abolitionist movement.
for dixie partisans the war was a battle for FREEDOM from a faraway government which southerners increasingly viewed as intrusive & potentially dictatorial. they wanted OUT of the union AND were willing to die to be FREE. (the soldiers,sailors & marines of the CSA saw themselves as being exactly the same as the heroes of 1776.)
for unionists, the war was to prevent the union being divided. dedicated unionists were prepared to die to prevent the south departing. (MANY thousands of those BRAVE union boys DIED BRAVELY in a POOR CAUSE.)
it really was NO MORE complicated than that.
99% of EITHER side cared NOT a DAMN about "the pitiful plight of the slaves". (BOTH sides SHOULD have cared. they DID NOT care!)
99% of Americans wouldn't have fought a SKIRMISH over slavery in 1861. hardly ANYONE would have fought a WAR that killed a MILLION people over the DYING "peculiar institution" even in 1864. (furthermore, veterans on BOTH sides would have lol AT you had you told them that that was what the war was about!)
all this talk of "slavery was a major cause of the war" is in a word: BALDERDASH (and/or: a KNOWING LIE, told NOW, by sanctimonious,REVISIONIST, DAMNyankee, LEFTISTS!)
free dixie,sw
it was lincoln's WAR & the blood of a MILLION Americans was/IS undeniably on HIS hands.
free dixie,sw