Look, I'll keep the recommendation in mind, & I agree re the horror & folly of the war, but there was no single battle in which one million men were killed. If the documentary holds this, they're mistaken.
The Battle of the Somme (140 days) July-Nov 1916 over 1 million killed.
The term battle today usually means maybe a week at most to decide a victor.
The historian interviewed stated that the length and casualties were so great, Somme and Verdun actually changed the meaning of the word 'battle'. It was called a battle at the time.
"They we so big, it crossed the threshold of suffering"