June 3. Cold Harbor. I was killed.

This entry was written by an unidentified Civil War soldier. And yes, indeed, he died from his wounds. His diary was found with his dead body, it was blood spattered.

Another, Joseph Hume, kept a diary. He sadly died and his doctor wrote at first in his (Joseph's) diary: "Joseph received his death wound," then after Hume's death:"Joseph died of consequence of above."

It's true that most Civil war soldiers died because of infections or illness. But it is important not to think that they were infantile in their medical knowledge.  In the 1600s, medicine was evolved enough to set bones (but they still couldn't conquer the Black Plague).

Joseph's Diary, last entries shown

Civil War Complete Surgical Set