This hymn was born during the American civil war, when Howe visited a Union Army camp on the Potomac River near Washington, D. C. She heard the soldiers singing the song "John Brown's Body," and was taken with the strong marching beat. She wrote the words the next day:

I awoke in the grey of the morning, and as I lay waiting for dawn, the long lines of the desired poem began to entwine themselves in my mind, and I said to myself, "I must get up and write these verses, lest I fall asleep and forget them!" So I sprang out of bed and in the dimness found an old stump of a pen, which I remembered using the day before. I scrawled the verses almost without looking at the paper.

The hymn appeared in the Atlantic Monthly in 1862. It was sung at the funerals of British statesman Winston Churchill, American senator Robert Kennedy, and American presidents Ronald Reagan and Richard Nixon.

Source: The Cyberhymnal