Robert Axelrod's "evolution of co-operation" book on Game Theory discusses instances of German and Allied trench forces in WWI firing their artillery at the same time and place each day so it looks and sounds like a war is happening but the poor schmucks on the front line aren't needlessly murdering each other. It supposses they can organize this without any explicit communication as it's fairly obvious when someone is trying to kill you.

There's also a long history of people in wars not even firing their weapons covered in the book "On Killing". People generally don't want to needlessly kill other human beings and a big part of army training and tactics is to work around this basic human instinct e.g. making you fight to keep your small group of friends alive, rather than for the financial benefit of some oligarch hundreds of miles away in safety.