It is not like the the “Declaration of the Immediate Causes Which Induce and Justify the Secession of South Carolina from the Federal Union” mentions the right to own slaves a dozen times.
it only declares their right to own slaves 6 times.
It is irrelevant. Slavery was legal in both the North and the South, and the Federal government did not invade the South to stop it. Saying it did is just ignorant. (or dishonest.)
The reason why the North invaded the South was because an independent South was going to trade directly with Europe and the business of New York and the Tax Collectors of Washington, were both going to be left out in the cold.
The South produced the vast majority of all export value to Europe. Between 73 and 84% of the total of US export goods came from the South, and the US was going to lose 200 million dollars per year as a consequence of Southern Independence.
Worse, the extra capitalization of the South would have funded competing Industries against the Northern Industrial barons, and the low tariffs of the Confederacy would have had the western territories saturated with European goods at far cheaper prices than what the Northern industries could provide.
Letting the South become independent would have been a financial disaster for the economic conditions in the Northeast, where the powerful and wealthy Lincoln backers lived.
And *that* is the cause of the war. If it had been about slavery, they would have started with the Union slave state Maryland.
If it had been about Slavery, Lincoln wouldn't have supported the Corwin amendment, and the Northern states wouldn't have been lined up to pass it.
If it had been about Slavery, the Emancipation Proclamation would have been issued in April of 1861 instead of 1863.