What advancement would have been directly responsible for the army that protected the city of Thebes?

The advancement that would have been directly responsible for the army that protected the city of Thebes was the development of the hoplite phalanx. This military formation, characterized by heavily armed infantry soldiers (hoplites) arranged in tightly packed rows, allowed for effective combat and defense in battles. The use of armor, shields, and long spears in this formation provided both offensive and defensive capabilities, contributing to the strength of Thebes' military during its height. Additionally, strategic alliances and training further enhanced the effectiveness of Theban forces.