Geography was very important during the Civil War. Because Washington, D.C. was surrounded by southern states, it was essential that President Lincoln keep Maryland in the Union after Virginia seceded. If Maryland also seceded, Washington, D.C. would have been cut off from the North. President Lincoln arrested Maryland lawmakers who might have supported secession. As a result, Maryland stayed in the Union.
The South was very dependent on bodies of water for trade and for the movement of people and products. The North imposed a blockade on the South that became more effective as the war progressed. The South found it harder to get needed supplies into the Confederacy. They also found it much more difficult to trade with other countries. The Union blockade was quite effective.
The Mississippi River was very important to the South. If the North got control of the Mississippi River, the South would be divided. The states west of the Mississippi River would be cut off from the states east of the Mississippi River. Trade and transportation would be greatly impacted if this occurred. When the Union won the Battle of Vicksburg, the Union had complete control of the Mississippi River. This battle is considered one of the turning point battles of the Civil War.
Geography played a key role in helping to determine the eventual winner of the Civil War.