If you could send modern generals back in time, with their casualty-averse philosophy, I think the bulk of them would decide to stay on the defensive. If the enemy is willing to throw a million men away, let him.
Another thing I wonder about which is probably stupidly risky is forcing the war to go mobile again. WWI started out as all the experts said it would, with a speedy advance and a mobile defense. Then things got bogged down when the Germans were stopped in the Battle of the Marne. The French probably couldn’t afford to do this given how close they were to Paris, but I wonder if the Germans might not have profited from pulling up stakes and going back to within a few miles of the German frontier bordering Belgium and see if they could get the Brits and French to also pull up stakes and pursue them? Once the bulk of neither side is dug in, maybe they get things moving again.
Also, the war wasn’t a stalemate anywhere but the Western Front, where massive forces faced each other in a relatively small geographic area. Perhaps the Kaiser shouldn’t have been such a pussy about his very expensive navy and engaged the British directly for control of the seas. Then he could have landed forces at will anywhere in France or even take the war to Britain.
It seems to me that both sides were reluctant to take any risks except to throw young lives away. Forget a modern general, I bet Douglas MacArthur would have had an Inchon up his sleeve if he’d been in charge.