For example, if you read the entire Texas Declaration, you'll see there were three or four major issues leading Texans to secede, of which the preservation of slavery was only one.
But when you read it,the Texans make it overwhelmingly about slavery, and even the issues that they mention that might not be directly related to the peculiar institution, THEY THEMSELVES relate to it.
When the issue of tariffs is mentioned (without using that word), it isn't as with "the agricultural product exporting states" that Texas identifies itself. No, it's
They have impoverished the slave-holding States by unequal and partial legislation, thereby enriching themselves by draining our substanceEven when they complain about the lack of military support against the Indians (ironically, by the way, seeming to demand a larger federal presence) what they say is:
They have refused to vote appropriations for protecting Texas against ruthless savages, for the sole reason that she is a slave-holding State.The fact is that the word slave (or slavery, or slave-holding) appears 21 TIMES in the Texas declaration, and in fact is one of the most frequently appearing words in that document
They have refused to vote appropriations for protecting Texas against ruthless savages, for the sole reason that she is a slave-holding State.(Emphasis yours.)
I'm not sure you make your point the way you wanted it to be taken. That is, yes, the Texans are arguing that the Northern States' congressional representatives, in denying the military appropriation, made it clear that their reason for doing so, was that Texas was a slave State. It was the Northern politicians who made slavery the issue, when the issue Texas took with their having done that, was that it was a violation of the Constitution, viz., denying Texans the protection of federal troops, which was still extended to other States that were in better political odor with the Northern political faction.
Which is pretty much how the whole issue of slavery came to the fore in the first place. The Abolitionists made it an issue, and the Republican Party took up the cudgels for their own, somewhat different reasons.
There has been some recent scholarship on the subject of the Northern moral crusade against slavery, its content and the method and tenor of its propagation, that tells us a good deal about how the issue came to be such a large one.
Remember, slavery wasn't the issue in 1832 when North and South clashed over the 1828 Tariff. It was Northern politicians who sought to make it a sectional issue, and attached the slavery crusade to it (being a moral crusade, and therefore absolute, its appeal could never be appeased except by the destruction of its object), the better to unite their advantage in numbers, consolidate the North with the agrarian Midwest, and overwhelm their opponents in the Congress and take over the federal government, which at length they did, after the slavery issue neutralized Northern exponents of the National Democracy like Stephen Douglas. Douglas had been a viable future presidential candidate when he helped engineer the 1850 Compromise, but his political career was utterly destroyed by the slavery issue and Kansas-Nebraska. Kansas-Nebraska was his effort to straddle and finesse the slavery issue being pushed by Free Soilers and Northern Whigs. Lincoln not only unhorsed Douglas but wrecked his party with the slavery issue.
That is why slavery was an issue in 1860: because the Republicans and Free Soilers insisted on making it the paramount issue, when thanks to Henry Clay and the 1820 Missouri Compromise, it hadn't been before Texas's (denied) application for statehood in 1836. The territorial gains of Texas annexation and the Mexican War required it to be put to bed again with the 1850 Compromise, but after Kansas-Nebraska and Dred Scott, Lincoln and the Republicans set sail on a policy of "no victory, no peace", when Lincoln gave the 1858 "House Divided" speech, the implications of which were clear: that no matter what he said about the extension of slavery, Lincoln was committed to the extinction of slavery, and therefore the extinction of the cotton economy and with it the livelihood of the agrarian South.