Complex sentence: The Pope was often compelled to defend the Church by waging war, equipping martial expeditions, or at least financially assisting the princes who waged such wars at his exhortation, but the Papal treasury was often insufficient to defray even the expenses of the Papal States.
Split into simpler sentences: The Pope was often compelled, in defense of the Church, to wage war, to equip expeditions, or at least to give financial assistance to the princes who waged such wars at his exhortation. But the Papal treasury was often insufficient to defray even the expenses of the Papal States.