Can an inferior kingdom defeat a superior kingdom militarily?
No. Militarily, an inferior kingdom simply does not defeat a superior one; it just does not happen. The inferiority described in the metal progression refers not to military strength but to political greatness, so Babylon's successor would defeat it politically, not by superior military power.
Les explains that when he first started teaching this years ago, the word "inferior" bugged him because he wondered how an inferior kingdom could defeat a superior one. He concludes that militarily it just doesn't happen. The metal progression moves from what is normally thought of as the most precious and expensive down to the least, from something great to something less great. Therefore, the prophet's statement that a kingdom inferior to Babylon would defeat them was not about military strength but about political strength.