If we're going to nitpick, then the South shooting first is as propagandistically misleading as saying Germany shot first in WWI or Japan in WWII. Yes, it's true, if you ignore the things like supplying arms to Britain or embargoing Japan or lying to the South about evacuating Ft. Sumter:

"He stated that Mr. Seward authorized him to give assurances to the Southern commissioners that Fort Sumter would be evacuated. This assurance appears to have been repeated, on various occasions, and at length with the statement that the fort would be immediately evacuated. On the seventh of April, Mr. Campbell, having learned, doubtless, that ships-of-war were in motion at New York and elsewhere, and hearing the rumors at Washington, addressed a note, indicating his uneasiness, to the Secretary of State, and received the explicit reply: "Faith as to Sumter fully kept - wait and see." On the twelfth of April, a fleet, consisting of two sloops-of-war, a steam cutter, and three steam transports appeared off Charleston harbor, and remained at anchor in the offing, inactively, during the assault which ensued. It is well known that upon the appearance of this fleet, a message was despatched to Montgomery for orders, to which the reply was, to demand the surrender of the fort, and to reduce it if compliance with the demand were refused. Upon Major Anderson's refusal, the bombardment began."

The thing is, the War between the States really truly was about slavery, nothing else.

It's a bit more complicated than that.

I was struck by one quote from Lincoln's first inaugural address (emphasis added):

"The power confided to me will be used to hold, occupy, and possess the property and places belonging to the Government and to collect the duties and imposts; but beyond what may be necessary for these objects, there will be no invasion, no using of force against or among the people anywhere. Where hostility to the United States in any interior locality shall be so great and universal as to prevent competent resident citizens from holding the Federal offices, there will be no attempt to force obnoxious strangers among the people for that object. While the strict legal right may exist in the Government to enforce the exercise of these offices, the attempt to do so would be so irritating and so nearly impracticable withal that I deem it better to forego for the time the uses of such offices."

In other words, as long as they rendered unto Caesar and didn't take his stuff, Lincoln was willing to abandon all other federal government functions no matter how constitutionally mandated. This seems like secession in all but name.

Remember also that the casus belli was that Fort Sumter was supposed to be handed over to the Confederacy, but the federal government refused to.

Both seem more consistent with a power theory than a slavery theory.

The thing is, the War between the States really truly was about slavery, nothing else.

Not about expanding or preserving the personal power of the most prominent decision makers? Wow. The war between the states sounds truly exceptional!

The thing is, the War between the States really truly was about slavery, nothing else.

I am suspicious of any monocausal theory of historical events. Surely slavery is by far the most important cause of the war. But there were a lot of other reasons.

The North (well, congress) tried to buy out the South (well, slaveowners). The South rejected it. There were actually mulitple attempts at this, some before the war, some during the war.

I did not know that, though I am not greatly surprised. Do you have a source where I can learn more?