I think what @Renohren@lemmy.world’s referring to is that India and Pakistan have, in the past, conducted nonviolent ceremonies at the border involving soldiers from each side.

https://www.youtube.com/watch?v=LixwXJpggME

I believe that the painting that you’re talking about was from an American Civil War battle that was close enough to a city (Washington DC?) that spectators decided to show up to watch. A bunch of people (including, IIRC, spectators) did die. That wasn’t being done with the intent of ceremony.

kagis

The First Battle of Bull Run.

https://www.history.com/articles/worst-picnic-in-history-was-interrupted-by-war

On July 21, 1861, Washingtonians trekked to the countryside near Manassas, Virginia, to watch Union and Confederate forces clash in the first major battle of the American Civil War. Known in the North as the First Battle of Bull Run and in the South as the Battle of First Manassas, the military engagement also earned the nickname the “picnic battle” because spectators showed up with sandwiches and opera glasses. These onlookers, who included a number of U.S. congressmen, expected a victory for the Union and a swift end to the war that had begun three months before.

Instead, the battle that day resulted in a bloody defeat for the Union and sent the picnickers scrambling to safety.

Just to confirm, Tineye finds one match corresponding to your image, called “CivalWar_PicnicAtManassas.jpg”, so I suspect that’s from that battle.

I don’t think that I’d call that very representative of even American Civil War battles, though, much less of all prior battles in history.