There were slaves in Deleware up till the 1860s. There were slaves in a lot of Northern states, but the great body of people in the North were not concerned so much with these small bits of slavery here and there, they objected mostly to the large scale plantation farming that employed thousands of slaves.
They would have tolerated this small scale slavery in the territories just as much as they tolerated it in their own states, were it not for the hyped propaganda which had them believing new plantations would be opening up in the territories.
It appears more and more that the whole "expansion of slavery" argument was just histrionic astroturf.
Read your own article. There were 18 slaves left in New Jersey in 1860, and none in the states to the north or east. That is not a lot.
They would have tolerated this small scale slavery in the territories just as much as they tolerated it in their own states, were it not for the hyped propaganda which had them believing new plantations would be opening up in the territories.
It's not really the same thing. 18 or 236 slaves with no prospect of more slaves or new slaves is different from several thousand slaves with prospects for more new slaves. Northerners really might not have cared if Kansas had 200 or 20 people enslaved for the rest of their lives with no possibility of additional slaves.
If Kansans and Nebraska had slaveowners who were reconciled to the fact that slavery was becoming a thing of the past, other Americans probably would have been reconciled to that. But if Kansas and Nebraska had slaveowners who were committed to the growth and expansion of slavery - even into free states - of course those in the free states would be concerned.
George Washington would have felt the same way. He was a slaveowner uneasy with the idea of slavery, a slaveowner who hoped the institution would eventually disappear. Some people say the same thing about Robert E. Lee. Whether that's true or not, it's hypocritical if you respect such men and attack Northerners for attitudes that weren't entirely different.
Delaware was a Southern slave-state, though with fewer slaves than any other slave-state.
Delaware's slave population fell from 9,000 in 1790 to fewer than 2,000 in 1860, while its freed-black population rose from 4,000 in 1790 to 20,000 in 1860.
But Delawareans refused to secede in 1861, refused to abolish slavery on their own and refused to even ratify the 13th amendment until ~1902.
DiogenesLamp: "There were slaves in a lot of Northern states..."
The total number of slaves in Northern states fell from 40,000 in 1790 to just 18 in 1860.
At the same time the population of Northern freed-blacks rose from 27,000 to 226,000.
DiogenesLamp: "...the great body of people in the North were not concerned so much with these small bits of slavery here and there, they objected mostly to the large scale plantation farming that employed thousands of slaves."
The "great body of people in the North" wanted zero slaves -- none, zip, nada slaves -- in their own states and in western territories.
Most were generally satisfied to let slavery continue in states where it was already legal, believing that eventually those states, like their own, would come to see slavery as wrong and abolish it, on their own.
But the SCOTUS Dred Scott ruling opened many eyes and raise realistic fears that, as Lincoln said in 1858:
DiogenesLamp: "They would have tolerated this small scale slavery in the territories just as much as they tolerated it in their own states, were it not for the hyped propaganda which had them believing new plantations would be opening up in the territories."
The issue was fought out in Kansas with the 1860 census result: 2 slaves and 625 freed-blacks in Kansas territory.
White Kansans did not object to blacks, but did want slavery eliminated in their territory.
DiogenesLamp: "It appears more and more that the whole 'expansion of slavery' argument was just histrionic astroturf."
There was nothing "histrionic" or "astro-turf" about "bleeding Kansas" in the 1850s.
Rather there was a serious contest to see whether slavery or freedom would rule the territory, and slavery almost won, thanks to help from Washington, DC, Democrats.
Even in Illinois slavery was debatable, as the 1837 legislation condemning abolitionists (which Lincoln was one of very few to oppose) clearly demonstrated.
Indeed, Illinois used slaves at its Gallitin County salt works officially until 1825 and with subterfuge thereafter.
So there was nothing "histrionic" or "astro-turf" about it.