On the 4th of February, 1861, the Confederate Congress, composed of delegates from the six southern states met at Montgomery, Alabama and completed the secession movement by composing and adopting their own constitution. This ended the slavery problem for the Union states.
The issue of slavery no longer had any political influence or social impact on the Union states or the territories. Those that remained preoccupied with it were needing a rationalization for their personal issues.
And that is exactly what started the war. No more slave-produced profit money for them.
New York City, not just Southern cities, was essential to the cotton world. By 1860, New York had become the capital of the South because of its dominant role in the cotton trade. New York rose to its preeminent position as the commercial and financial center of America because of cotton. It has been estimated that New York received forty percent of all cotton revenues since the city supplied insurance, shipping, and financing services and New York merchants sold goods to Southern planters. The trade with the South, which has been estimated at $200,000,000 annually, was an impressive sum at the time.
http://mshistorynow.mdah.state.ms.us/articles/161/cotton-in-a-global-economy-mississippi-1800-1860
Only a small percent of Northerners were "preoccupied" ardent abolitionists.
For the rest, they were content to "live & let live", so long as slavery seemed to be progressing towards gradual abolition.
What they didn't want was the Slave Power pushing its "peculiar institution" into their own states via Supreme Court rulings (Dred-Scott) or Federal fugitive slave law enforcement.
When seven Deep South states declared secession, that certainly eliminated the Slave Power's hold over Congress, but those old Northern concerns were quickly replaced by the new specter of Confederate military might (100,000 Confederates versus 17,000 Union troops) threatening United States existentially.