My understanding is that all the events that created tension between North and South were directly or indirectly related to slavery, and without the growing abolition movement and the controversy over the expansion of slavery to new states, the Civil War never would have happened.
But I've been hearing a lot from the "states' rights" crowd lately claiming slavery was NOT the main cause of the Civil War. Were there any specific issues not related to slavery/abolition that caused resentment in the South? Were there any other specific "rights" not related to owning slaves that Southern leaders felt were threatened? Did they reference these issues or rights in any speeches or documents?
Your understanding that slavery was the principal cause of the civil war is correct. There were issues present like the tariff, internal improvements, and the cause of "states' rights," but all of them were intimately tied to the slavery question. In this light, it's important to look at the Southern states' declarations of secession to see what really motivated the Confederates.
Because seriously, if you want to know why the Confederacy left the union, their legislatures wrote down the official reasons and published them for public consumption at the time of secession!
The Presidential election of 1852 resulted in the total overthrow of the advocates of restriction and their party friends. Immediately after this result the anti-slavery portion of the defeated party resolved to unite all the elements in the North opposed to slavery an to stake their future political fortunes upon their hostility to slavery everywhere. This is the party two whom the people of the North have committed the Government. They raised their standard in 1856 and were barely defeated. They entered the Presidential contest again in 1860 and succeeded.
The prohibition of slavery in the Territories, hostility to it everywhere, the equality of the black and white races, disregard of all constitutional guarantees it its favor, were boldly proclaimed by its leaders and applauded by its followers.
With these principles on their banners and these utterances on their lips the majority of the people of the North demand that we shall receive them as our rulers.
The prohibition of slavery in the Territories is the cardinal principle of this organization.
In the momentous step which our State has taken of dissolving its connection with the government of which we so long formed a part, it is but just that we should declare the prominent reasons which have induced our course.
Our position is thoroughly identified with the institution of slavery-- the greatest material interest of the world. Its labor supplies the product which constitutes by far the largest and most important portions of commerce of the earth. These products are peculiar to the climate verging on the tropical regions, and by an imperious law of nature, none but the black race can bear exposure to the tropical sun. These products have become necessities of the world, and a blow at slavery is a blow at commerce and civilization. That blow has been long aimed at the institution, and was at the point of reaching its consummation. There was no choice left us but submission to the mandates of abolition, or a dissolution of the Union, whose principles had been subverted to work out our ruin.
We affirm that these ends for which this Government was instituted have been defeated, and the Government itself has been made destructive of them by the action of the non-slaveholding States. Those States have assume the right of deciding upon the propriety of our domestic institutions; and have denied the rights of property established in fifteen of the States and recognized by the Constitution; they have denounced as sinful the institution of slavery; they have permitted open establishment among them of societies, whose avowed object is to disturb the peace and to eloign the property of the citizens of other States. They have encouraged and assisted thousands of our slaves to leave their homes; and those who remain, have been incited by emissaries, books and pictures to servile insurrection.
We hold as undeniable truths that the governments of the various States, and of the confederacy itself, were established exclusively by the white race, for themselves and their posterity; that the African race had no agency in their establishment; that they were rightfully held and regarded as an inferior and dependent race, and in that condition only could their existence in this country be rendered beneficial or tolerable.
That in this free government all white men are and of right ought to be entitled to equal civil and political rights; that the servitude of the African race, as existing in these States, is mutually beneficial to both bond and free, and is abundantly authorized and justified by the experience of mankind, and the revealed will of the Almighty Creator, as recognized by all Christian nations; while the destruction of the existing relations between the two races, as advocated by our sectional enemies, would bring inevitable calamities upon both and desolation upon the fifteen slave-holding states.
By the secession of six of the slave-holding States, and the certainty that others will speedily do likewise, Texas has no alternative but to remain in an isolated connection with the North, or unite her destinies with the South.