A big reason why they didn't want to be a part of the US was because they didn't trust the Republicans to respect slavery. As I've said over and over -- and as historians have said -- they feared that Lincoln could use his appointment power to build up an anti-slavery Republican Party in the South.
I can't think of any where there was a great deal of separation between New York and the Great Lakes states.
Even in the maps you show, the elections of 1960, 1968, 1976, and 1988 do show some of the Great Lakes States voting differently from the Midatlantic Tristate area. The same was true in 2016. Maps from the FDR era (say, 1928-1948) reveal a variety of different patterns. New York's FDR was a hero to the South and not that popular in the Midwest. Going back further into the late 19th century, the South voted as a solid bloc, and the North voted almost as a bloc. People remembered which side they fought on in the Civil War. But when Democrats did win, it's because of the swing states: New Jersey, Indiana, sometimes Connecticut, and New York above all. New York City's real electoral alliance was with the South. That started with Jefferson and Burr in 1800 and ended with Carter and McGovern in the 1970s.
There is some overlap in the voting between the Northeast and the Midwest. They were early industrializers and now they are old industrial/urban states. They had similar ancestry. They both fought for the union. But there were also serious rifts between the two. It's folly to think that Illinois or Wisconsin or Michigan were only singing New York City's tune in 1860. Such states were mostly agricultural then and no more beholden to New York City than the Southern states. In fact, a good deal less. Twenty or thirty years before, Michigan and Wisconsin had been the West. Cities there were small, and the largely agricultural population was quite independent minded.
But if you just want one big idea to explain everything, details don't matter.
Perhaps, but I think it is a big mistake to dismiss the financial angle in any effort to understand what is happening in any sort of political issue.
As I've said over and over -- and as historians have said -- they feared that Lincoln could use his appointment power to build up an anti-slavery Republican Party in the South.
I understand the concept of allowing unelected federal bureaucrats to "regulate" something they don't like to death, so this is not an idle fear, but again I think the financial end of this would have created pushback from the people making their wealth as a result of slavery (and I mean people in the North as well as the South) and it would not likely have materialized as anything significant.
Even in the maps you show, the elections of 1960, 1968, 1976, and 1988 do show some of the Great Lakes States voting differently from the Midatlantic Tristate area.
I noticed that, but those would appear to me to be special cases, and the map doesn't provide the details of how significantly they differed. It may have only been a few percentage points.
The same was true in 2016.
Trump made heavy inroads into the working class "rust belt" Union members, and that's why he won Michigan, etc.
Maps from the FDR era (say, 1928-1948) reveal a variety of different patterns.
I looked at those. FDR was a phenomena, and of course he was going to get reelected to a 3rd and 4th term. Did you look at the maps from 1900?
Going back further into the late 19th century, the South voted as a solid bloc, and the North voted almost as a bloc.
Yes they did and I suspect a lot of that was just keeping up the hatred for the other side. I think remnants of that pattern have been affecting elections perhaps even to the present day.
New York City's real electoral alliance was with the South. That started with Jefferson and Burr in 1800 and ended with Carter and McGovern in the 1970s.
New York was making a lot of money off of the South, but they were also making a lot of money from the industrialized great lakes states. (Midwest) They wanted both of those sources of money to keep flowing.
It's folly to think that Illinois or Wisconsin or Michigan were only singing New York City's tune in 1860. Such states were mostly agricultural then and no more beholden to New York
Look up the "Graingers."
But if you just want one big idea to explain everything, details don't matter.
There is a lot of noise in the data, but there is also what I see as a pretty strong "signal" if you understand how those references apply.
New York is a concentration of economic and political power and it always has been. It exerts outsized influence on the rest of the nation and especially on states that use it or rely on it for revenue.
So if New York votes to keep slavery, there is a fair chance that it will convince it's economic allies to do so as well.