There were 4 "Loyal Union States" that had slaves, and none of them were "Northern". All four were referred to at the time as "Border States" --- Missouri, Kentucky, Maryland and as you said, tiny little Delaware.
None seceded from the Union for the simple reason that the 30 years of arguments over expansion that culminated with the election of Lincoln had little to do with the economics of those states. Slavery was simply not what the majority relied on for their livelihood in those 4 states.
It was a direct correlation between the economic importance of expansion and the economies of the states (even counties) to the fervor for secession. Virginia is a great example. In the Eastern tidewater where slave population was very high and slavery was a still money making proposition, secession was "popular." In the Western mountain counties with very few slaves and the beginnings of heavy industry along the Ohio Valley, there was so little support for secession, they ended up telling the Eastern aristocrats in Richmond to go the hell and created their own state of West Virginia. The Slave Power did not rule the Hill Billies.
BTW. I am damn sick and tired of hearing the neo-confederate bs from the historically illiterate that there were "Northern Slave States." None of those states were "Northern" so strike that bit of misinformation from you list of favorite fantasies.
BTW. If the Confederacy was not about slavery, were there any Confederate "Free States"? Can you name one?
The 4 previously mentioned states remained in the Union. The other states seceeded to form the Confederacy. Union states are commonly referred to as Northern. Simple.
Try asking it this way: If the Union was fighting to free slaves, were there any Union Slave states? You mentioned them in your previous post.
"There were 4 "Loyal Union States" that had slaves,"
FYI Missouri voted to secede and her secession was accepted by the newly constituted Southern government. She was counted as the 12th star on the Battle flag.
http://members.tripod.com/2ndmocavcsa/id14.htm