Maryland, Delaware, Missouri, and Kentucky
It was one of the four slave-states of the Upper South that stayed loyal - a big issue with Lincoln.
It was the border states that didn't secede (or leave) to the Confederate United States of America. For example Tennessese didn't secede but decided to run to governments at the same time, one Union Government and one Confederate Government. Kentucky did the Same thing
After a short time they joined the Union side and fought against the Confederacy. However a part of their citizen, especially those of Missouri and Kentucky, enlisted themselves voluntarily in the Confederate Army.
These were the two biggest border-states - that is, slave-states of the Upper South, that had stayed loyal to the Union. With these states, Lincoln had to be especially diplomatic, to persuade them not to go Confederate.
The North had abolished slavery, because it did not fit the industrial system. In the Civil War, four slave-states stayed loyal to the Union, and were counted as 'the North'.
They were the slave-states that stayed loyal to the Union. Lincoln treated them tactfully, and allowed them to continue practising slavery during hostilities, for fear of driving them into the arms of the Confederacy.
Missouri, Kentucky, Maryland, and Delaware. Slaves in these states were not freed till after the US Civil War; not even by the Emancipation Proclamation. These four states were the slave border states and purposefully not included in the Emancipation Proclamation. US President Lincoln could not risk having these states join the Confederacy.
Kentucky, Missouri, Maryland, Delaware
15 slave states and 19 free states during the American Civil War
1. Secesh states 2. the South 3. Dixie
Missouri, Kentucky, Maryland, and Delaware. West Virginia was also formed during this time period and remained loyal to the Union. Slaves in these states were not freed till after the civil war; not even by the Emancipation Proclamation.