Short answers, pulled from the story.
The melody emerged during the late 18th and early 19th century within American camp meeting gatherings. These events occurred in frontier areas where people worshipped before traveling preachers arrived.
George Kimball stated that the 2nd Infantry Battalion of the Massachusetts militia known as the Tiger Battalion collectively created the lyrics. Leaders within the battalion felt the original lyrics were coarse but could not stop their adoption.
Freed African Americans and white missionaries held a parade of 10000 people led by 3000 Black children singing John Brown's Body on the 1st of May 1865. This march honored 257 dead Union soldiers whose remains were reburied from a mass grave in a Confederate prison camp.
Julia Ward Howe wrote Battle Hymn of the Republic when a friend suggested she write good words for that stirring tune. William Weston Patton published his influential version in the Chicago Tribune the 16th of December 1861 after composing it in October 1861.
Italian singers Gino Negri and Milva recorded versions on albums including Canti della libertà released in 1965 while Pete Seeger recorded his widely circulated version in 1959. University of Pennsylvania adopted the tune for a fight song beginning Hang Jeff Davis from a sour apple tree.