Desperation was the mother of stupid decisions; when one felt cornered, they tended to become anxious, and when humans became anxious, they generally did not think through their decisions properly before putting them into motion.
And this was the case for the French Army and their leadership. It was a tale as old as time itself, or at least as old as democracy… Politicians hid themselves away while starting wars neither they nor their privileged children had any intent to fight.
At least monarchs generally fought in the wars they started—or they had in years past. In fact, during Bruno's past life, the last national leader to fight in a war was actually King Albert I, who had rallied his forces and fought alongside them in a defensive operation against the Germans at the start of the Great War.