Answer:
A. He had trouble finding good generals.
Step-by-step explanation:
Lincoln faced the main problem with the Civil War, finding good generals. The majority of the generals sided with the Confederacy army when the confederate states seceded.
To solve the problem, Lincoln replaced generals and changed the structure of command in the army when he found Ulysses S. Grant that was important to the victories at Vicksburg, Mississippi and the West.