I've read this story in the 1990's, but I know that it was older than that, probably from the 60's or 70's.
In the story, the world is united under one government that is run by scientists, and most of the problems plaguing humanity have been solved thanks to advances in science and efficient resource management by the ruling council of scientists.
However, humans have become too dependent on it, and the world government realizes that they must do something about it. They end up organizing a reenactment of D-Day, with strict rules about the technology available to both sides and the help they can get, up to really executing spies caught.
What I remember from the book, possible spoilers if you haven't read it before:
The book opens with an astronaut on vacation being unable to land the small plane he was piloting because he wasn't getting any instructions. It was a clear sunny day, the astronaut had done that a thousand times before, there was nothing difficult, yet he couldn't land the plane. They had to create stormy conditions, with heavy cloud cover and rain, then guide him with precise instructions to finally make him land.
More similar events happen, making the government realize that something was wrong, and they quickly figure it out then get to work looking for a solution and end up with the idea of reenactment, in live conditions, of D-Day and everything that led to it. D-Day was chosen because it would involve and interest the whole world, even those not actively participating in it.
They set up the two sides plus a corps of arbiters to watch what is being done and ensure that no one is cheating by using technology or knowledge that wasn't available at the time, and is thus forbidden. Of course, and intense game of spying and cheating begins about immediately.
The whole of Normandy is cordoned off for the reenactment, with only the participants allowed to be there, everyone else is evacuated.
The battle starts as it did in reality, with heavy bombardment and artillery fire from the fleet at sea. Then someone uses a biological weapon, causing the battle to be stopped by the arbiters as they try to determine if that could have existed at the time. They allow it and the battle resume, then someone drops a nuclear weapon on the battlefield, exterminating all combatants, followed by a single paratrooper who lands at ground zero, deploys the flag of his side as the sign of their victory and dies because of the radiation.