Border states were those states, which were although slave states, yet they had chosen to remain part of the Union. The presence of these states and their display of loyalty to the Union was the main reason why President Abraham Lincoln did not talk about slavery initially as the chief goal of the American Civil War on part of the Union. Not only was the loyalty of the Border States important to the Union but also their position and location was verily crucial to the Union.
Specially after the victory of the Confederate army in the American Civil War when four border states joined the Confederacy, the remaining four became increasingly important for the Union. These Border States were Maryland, Kentucky, Delaware and Missouri. While Maryland and Delaware were significant in the context of their geographical proximity to the state capital Washington D.C., it were Missouri and Kentucky, who controlled the Mississippi and Ohio rivers, which were extremely important for the transportation of goods and soldiers for the Union army.
Specially after the victory of the Confederate army in the American Civil War when four border states joined the Confederacy, the remaining four became increasingly important for the Union. These Border States were Maryland, Kentucky, Delaware and Missouri. While Maryland and Delaware were significant in the context of their geographical proximity to the state capital Washington D.C., it were Missouri and Kentucky, who controlled the Mississippi and Ohio rivers, which were extremely important for the transportation of goods and soldiers for the Union army.