Why didn't the border states join the confederacy? (Short Animated Documentary) (Level 1)

When the American Civil War started in 1861, the country was divided. Eleven southern states left the United States to form the Confederacy. They wanted to keep slavery. However, four slave states stayed in the Union: Delaware, Maryland, Kentucky, and Missouri. These were called the "border states." President Abraham Lincoln knew these states were very important. If they left, the Confederacy would be too strong. Lincoln promised he would not end slavery in these states right away. This helped keep them loyal. Each state had a different story. Delaware had very few slaves and supported the Union. Maryland was very important because it was next to Washington, D.C. Lincoln sent soldiers there to stop people from leaving. Kentucky tried to be neutral. They did not want to fight. However, the Confederate army invaded them, so Kentucky joined the Union. In Missouri, the governor wanted to leave, but the Union army took control. In the end, staying in the Union helped these states survive the war.