Question

the first major union victory and one of the bloodiest battles of the civil war came at bull run. chancellorsville. fort sumter. antietam

Explanation:

Antietam was the first major Union victory and one of the bloodiest battles of the Civil - War. Bull Run was not a Union victory initially. Chancellorsville was a Confederate victory. Fort Sumter was the start of the Civil War, not a major Union victory battle.

Answer:

Antietam