Final answer:
The major Northern victory during the early stages of the Civil War was at the Battle of Shiloh, which was a significant Union victory despite the high number of casualties.
Step-by-step explanation:
The only major Northern victory during the early stages of the war came during the Battle of Shiloh. This battle took place in April 1862 and resulted in a significant Union victory. Despite it being a victory, the Northern press criticized General Grant rather than celebrate the triumph because of the high casualty rates.
The Battle of Antietam, however, was also a pivotal battle and significant in its own right as it led to the issuance of the Emancipation Proclamation. While it was not categorised as a clear Union victory, the Battle of Antietam was crucial in halting Lee's advance into the North and remains the bloodiest single day in American military history.
Therefore, the correct answer is c. Shiloh.