Pictures of guys blowing other guys' heads off! Being run through with swords! Being impaled on spears! Wonderful visuals for the baby-to-toddler set!
OK seriously if I were going to do this, I might try to make it sort of a game...the opposing generals and countries each have their own slide, then where it happened, then "Who won?" "England!" (and the general) or whatever.
So, for instance:
Battle of Waterloo [just those words on the slide]
Napoleon led the army of France. [pix of Napoleon and map of France]
The Duke of Wellington led the army of the United Kingdom. [pix of the Duke and the U.K.]
They fought the Battle of Waterloo right here. [map; perhaps adding: name of modern day country]
Who won? [just the words]
The Duke of Wellington and the U.K. won!
A lot of work, but otherwise I'm not sure there's any way to make it make sense or memorable to a child. They don't even know what a battle is...it's a very advanced concept because it requires they understand what countries, wars, fights, armies, etc., are.