It was France.
And this France was like an uncontrollable bomb even from the Allied perspective preparing for the next peace negotiations.
"Germany has already been halved, losing Poland. Russia has completely consumed East Prussia which was their origin, and Poland has separated from Germany becoming one after 122 years. Yet you want to take not just Alsace-Lorraine but the Rhineland and Saarland? Do you logically think Germany will accept that?"
"We must make them accept it! Yes, according to that national self-determination, we can at least set up puppet states as shells and stick them between Germany and France like Luxembourg! Would you accept that?"
"You're not making sense."
Though they had war plans, no country had even plotted how to handle the end of war and post-war arrangements.
Even Britain had only thought about taking over German colonies, not about executing Germany like France wanted.