Union troops changed the words to ‘Dixie’ to make fun of the South
Making fun of the enemy is nothing new, especially for American troops. When U.S. troops like something, they'll probably still come up with their own term for it. Even if they respect an enemy, they will still come up with a short, probably derogatory name for them. For American troops in the Civil War, many of which took the war very seriously (and rightly so), they would take any opportunity to denigrate the "Southern Way of Life." That started with the pop song "Dixie," which became a de facto national anthem for the Confederates.
But even Abe Lincoln loved the song. Why? It was written in New York for use in traveling shows.
"Dixie" was actually written by an Ohioan, destined for use among blackface performers in traveling minstrel shows throughout the United States. These shows were wildly popular before, during, and after the Civil War everywhere in the United States, and were usually based on the premise of showing African-Americans as slow, dumb, and sometimes prolifically horny. It's supposed to be sung by black people who are depicted as preferring life in the South, rather than as free men in the North.
"Dixie" is one of the most enduring relics of these shows, still retaining popularity today, although without the connection to the minstrel shows of the time. It's safe to say almost every Confederate troop knew the words to "Dixie," as the song depicts an idyllic view of what life in the American South was like in the 1850s, around the time the song was written, with lyrics like:
Oh, I wish I was in the land of cotton
Old times there are not forgotten
Look away! Look away!
Look away! Dixie Land!
Union troops who were dead-set on killing Confederates, eventually came up with some new lyrics for the song. Like a group of murderous Weird Al fans, the Northerners wanted to poke fun at their deadly enemy in the best way they knew how – a diss track. The Union lyrics are harsh and the tune to the song just as catchy.
"Away down South in the land of traitors
Rattlesnakes and alligators...
... Where cotton's king and men are chattels,
Union boys will win the battles...
Each Dixie boy must understand
that he must mind his Uncle Sam..."
The Union version of "Dixie" rates somewhere between "When Johnny Comes Marching Home" and "Battle Hymn of the Republic" on the list of All-Time Greatest Civil War Songs That Make You Want to March on Richmond.