The "Battle Cry of Freedom", also known as "Rally 'Round the Flag", is a song written in 1862 by American composer George Frederick Root (1820–1895) during the American Civil War. A patriotic song advocating the causes of Unionism and abolitionism, it became so popular that composer H. L. Schreiner and lyricist W. H. Barnes adapted it for the Confederacy.

A battle cry or war cry is a yell or chant taken up in battle, usually by members of the same combatant group. Battle cries are not necessarily articulate, although they often aim to invoke patriotic or religious sentiment. Their purpose is a combination of arousing aggression and esprit de corps on one's own side and causing intimidation on the hostile side. Battle cries are a universal form of display behaviour aiming at competitive advantage, ideally by overstating one's own aggressive potential to a point where the enemy prefers to avoid confrontation altogether and opts to flee. In order to overstate one's potential for aggression, battle cries need to be as loud as possible, and have historically often been amplified by acoustic devices such as horns, drums, conches, carnyxes, bagpipes, bugles, etc..