Final answer:
Clara Barton was the Union nurse who cared for the sick and wounded on the front lines during the American Civil War.
Step-by-step explanation:
The Union nurse who cared for the sick and wounded on the front lines was Clara Barton. Clara Barton was a pioneering nurse who served in the American Civil War and later founded the American Red Cross. She dedicated her life to providing medical care and humanitarian assistance to those in need.