While not specifically one battle, the Hundred Days Offensive was perhaps the most vital series of combat campaigns that ensured the collapse of the German empire. The Allied forces launched a series of offensive battles that would eventually result in depleted German morale, and the high commanders of the empire realizing they could no longer keep fighting an unwinnable war.
Why Include It?
The Hundred Days Offensive would not only serve as a plentiful backdrop for a narrative to explore, but what better way to win a game about war than actually winning the war? Being there on the front lines of seeing the Germans finally surrender, there would be no better feeling for a player to experience than actually being a part of the final battles.