Question

general
was forced to retreat at the battle of chancellorsville.
mcclellan
burnside
hooker

Explanation:

The Battle of Chancellorsville was a significant Civil War battle. General Hooker (Joseph Hooker) was the Union general who was forced to retreat at the Battle of Chancellorsville. McClellan was replaced before this battle, and Burnside was also not the one retreating here.

Answer:

Hooker (General Hooker was forced to retreat at the Battle of Chancellorsville)