Why did Clara Barton go into war?

She had already wounded her brother from a accident he had when he was a little boy she didn't go to school for 2 years so she could be by his side then she realized she loved helping people so when her brother got older and went into war she was a kid 13 years younger then him and he went in his teens she waited years and years so she could join as a nurse to help she joined at age 57.