Here's the backstory to a true American Christmas carol.

The poet Henry Wadsworth Longfellow wrote "Christmas Bells" (the carol we call "I Heard The Bells On Christmas Day") in 1863 in a depression over the death of his wife, who died from burns after her nightgown caught fire; and the severe wounding of his son (who enlisted without Longfellow's blessing) during the Civil War.

The poem reflects both his sadness over the war and the state of the world, his own personal pain, and his continuing hope in the power of God.

He wrote the poem on Christmas Day in 1863, after Gettysburg, but before it was clear that the war was turning, and there still remained no end in sight.

When we sing the song today, we almost always leave out some of the key verses explaining Longfellow's motivation for writing it, and so here it is with the missing stanzas restored:
I heard the bells on Christmas Day
Their old, familiar carols play,
and wild and sweet
The words repeat
Of peace on earth, good-will to men!

And thought how, as the day had come,
The belfries of all Christendom
Had rolled along
The unbroken song
Of peace on earth, good-will to men!

Till ringing, singing on its way,
The world revolved from night to day,
A voice, a chime,
A chant sublime
Of peace on earth, good-will to men!

Then from each black, accursed mouth
The cannon thundered in the South,
And with the sound
The carols drowned
Of peace on earth, good-will to men!

It was as if an earthquake rent
The hearth-stones of a continent,
And made forlorn
The households born
Of peace on earth, good-will to men!

And in despair I bowed my head;
"There is no peace on earth," I said;
"For hate is strong,
And mocks the song
Of peace on earth, good-will to men!"

Then pealed the bells more loud and deep:
"God is not dead, nor doth He sleep;
The Wrong shall fail,
The Right prevail,
With peace on earth, good-will to men."