.
By 1860, it was no longer north/south.
The annexed territories were booming in the west, and by then the Salinas valley in California was producing more food than all the rest of the country combined.
That was what gave the railroads so much power.
.
Oh dear, was that a typo, "1860"?
Did you mean to type "1960", because that's closer to what you describe?
In 1860 what you claim here was absolutely non-existent.
In 1860 there were no railroads connecting California to the East, nor was the Salinas valley in California more than sparsely settled.
All that came after the Civil War.
As for your larger point about it being no longer north vs. south by 1860, no, far from it if by "north" you mean free states and by "south" slave states.
In 1860 the South had long dominated Washington, DC, politics, but what changed then, for the first time after the election of November 1860, was Northern Republican electoral domination of Washington.
That was the sudden change which drove Southern Democrats to declare secession and eventually war on the United States.
I think your problem is you've imagined the US economy of, say 1890 or even 1930 as what was true in 1860 and that's absolutely not the case.
1860 was a very different United States.