The Central Powers had been given a string of victories, and only a single defeat nearly a year into the war. Had they simply pushed into Paris, Belgrade, and Constantinople from the start of the war, it would have been over by now.
But that would have resulted in the Allied Powers simply gearing up for round two. And if that could at all be avoided, Bruno wanted to do so.
The plan was to fight defensively, and use their overwhelming preparations to absolutely bleed the Allied Powers dry of their men and resources so that they simply could not wage war for decades.
And in doing so, buying Bruno and his enterprises enough time to ensure that Germany once more had an overwhelming technological advantage should that dreadful day finally come to pass.