Civil War Reenactment
Even though the first American Civil War reenactment probably took place during the 50th anniversary of the Battle of Gettysburg (including actual veterans), it wasn't until the 1961–1965 Civil War Centennial commemorations that this activity became widespread throughout the United States, and abroad as well, for instance in Canada, the United Kingdom, Germany, Australia, and Italy. One of the reasons behind reenactments is to gain an insight into the history of the country, and thus some reenacters strive to be as accurate as possible, even setting the mock battles in the same site that they originally took place, or as near as it possibly can be.
However, reenactments can't be to realistic either. To paraphrase Robin Williams, a Civil War Reenactment with live ammo would be similar to
buy Viagra and take some after an open heart surgery, not a good idea. Seriously though, there are different types of reenactors, from those who only scratch the surface to those who use the method acting approach and immerse themselves in the period that they are representing, so much so that in many instances of the events organized by the latter, the general public will not be admitted. Still, reenactments are among the most attended public events in the U.S.
These hardcore history buffs are usually the ones that producers and directors resort to when they need an extra hand for films like Gettysburg, Glory, and Gods and Generals. And though will even do it for free, reenactors and directors have often clashed over the accurate portrayal of a particular episode. Nevertheless, some filmmakers are more interested in simply having a large number of extras for massive battle scenes, which may lead to safety issues, though usually nothing that a trip to the nearest best pharmacy won't fix.