Roman military adaptation and Byzantine political infighting

Roman defeats could lead to adaptation, including adoption of the cataphracts that had proved effective against Roman forces. During the Republic and the empire's stronger periods, copying a successful enemy method could become the starting point for further innovation. Byzantine forces likewise remained capable when properly led and supplied. The interpretation offered here places greater weight on destructive internal politics than on simple military inferiority or supposed moral decline. Political disagreement became dangerous when defeating domestic rivals mattered more than resisting an external enemy. Explanations based on disliked lifestyles obscure that failure of collective defense.