I was building a Halloween costume of a 1980's-ish Soviet tank soldier when the thought occurred to me-- has war reenactment always been a 'thing'? I'm not talking about playing as a soldier (e.g. fighting with wooden swords in the backyard) or actual war fighting/war games. I'm talking about the kind of American civil war/WW/WWII reenactment groups that go to actual battlefields, have detailed costumes that match the period, etc. Thanks in advance!
YESSS! Something I actually know about! I did a lot of research on war reenactment in America using primary source documents over at the William L Clements Archive in Ann Arbor Mi.
In America it really is a 19th century invention by Civil War veterans. After the war, soliders from both sides would get together and talk about their experiences. Soon these gatherings became picnics, which then became encampments in original civil war military tents and outfits to try to explain the purpose and reasoning behind the war. It was also used as a way of trying to repair the nation (of course at the expense of any kind of racial explanation to the the causes of the way) by showcasing how bravely men fought on both sides without drawing any conclusions about right vs. wrong.
Here is the link to my article complete with sources: http://commons.emich.edu/mcnair/vol1/iss1/3/
I wrote in undergraduate school so if it's terrible, forgive me.
In imperial Rome 'reenactments' of events from military campaigns, even naval battles, were occasionally staged by Emperors. The main purpose however was for entertainment and public spectacle, not accuracy— the participants were often men already sentenced to death, dressed up in the costumes of different sides and forced to actually fight, as thousands of spectators looked on. From Suetonius' Lives of the Caesars, a description of an event put on by Claudius:
In the Campus Martius he staged the siege and destruction of a town, in the manner of an actual war, and also the surrender of the kings of the Britons, while he presided dressed in a general's cloak. Indeed, he even staged a sea-battle on the Fucine lake, when he was about to drain it... In this spectacle a Sicilian fleet fought against a Rhodian one, each made up of twelve triremes. (Suet. Cl. 21)
Here's some more information on the mock naval battles. Of course, this is a far cry from what you describe, where the participants are willing enthusiasts, and the purpose is reenacting an event exactly rather than just imitating circumstances and having a battle for show.