Final answer:
The Battle of Shiloh was the sole Union victory in the first year of the Civil War. Both sides realized early on that the war would not be a brief skirmish but a prolonged and costly conflict.
Step-by-step explanation:
The only Union victory during the first year of the American Civil War, which broke out in April 1861, was the Battle of Shiloh, which took place in April 1862. This significant battle along with Union forces capturing New Orleans and Memphis demonstrated that the Confederates were losing major ground on the western front. Both sides originally believed the war would be a short conflict, with a decisive battle settling the matters of secession and Union.
However, as the war progressed and the battles of Bull Run (First Manassas) reflected the harshness and ugliness of the war, both sides realized that the conflict would not be quickly resolved. The first year’s battles demonstrated a sort of military stalemate, where neither side could claim a decisive upper hand. This realization led to a reassessment, and it became clear that it would be a protracted and grueling struggle requiring significant mobilization and resources from both sides.