It was not long before the Allies were once more forced to flee from their position. They had made a critical error in assuming the Central Powers did not know exactly when, where, and how to hit the critical areas of defense.
Bruno had of course built the border complex to be damn near impenetrable from weapons of the era. There was just one thing the Allies weren't expecting. He also designed them to have secret passageways that could be utilized by his own forces should they ever be forced to abandon the complex.
A properly staffed, manned and supplied fortress would have remained unbroken for a decade, if not more. There was just one problem, a problem Germany had been plagued with in both timelines. And that was the incompetence of its allies.