This question is really opinion based, but I would take it personal when things go wrong, since I start to think what I didn't or did do that made things go wrong.
Answer:
What change made Byzantium more powerful? Defensive walls were built around the city. The region began to recover from civil wars. The emperor seized more power from the military.
Explanation:
Well I would personally say the engineering industry, as during the wartime technology needs to be developed/improved in order to defeat the opposing side.
