Complex sentence: The "strategoi" were appointed by the boule with the approval of Rome; the army, under the leadership of the monarch and the generals, was modeled on the Sasanians in arms and tactics.
Split into simpler sentences: The "strategoi" were appointed by the boule with the approval of Rome. The royal army was under the leadership of the monarch aided by generals, and was modeled on the Sasanians in arms and tactics.