Ulysses S. Grant was a key figure in the Civil War. After the Civil War, Grant became president of the United States. The reason Grant was so important during the Civil War is because he is known for leading the Union side to win the war. Grant was a key piece to the war. When the Civil War began, Grant had to decide which side he would lead.
The reason was many Civil War leaders on both the North and South sides went to the same school together. Grant and the others became educated at the United States Military Academy. Most of those who went to school with Grant decided to serve with the Confederacy. Very few Union leaders had the education and experience that Grant did.