Though you or another army might you will eventually find that a particularly heavily attacked site may have no loot remaining to give when you explicitly raid or pillage a place multiple times, there is nothing really stopping the site from simply making more goods during its fortnightly cycle for you to steal again that undercuts what they could offer you in tribute in a much slower-trickle.
To incentivize less of a repeated "pillage and repeat until they back down to agree peace", and to lay some groundwork I think this suggestion can help increase the frequency of razing and conquering by re-prioritizing what entities do and giving them a window in which to fufill it. If a hamlet has a loot capacity of 150, 151 soldiers would need to march on the hamlet to loot & raze in the same attack, or return multiple times in which every time afterwards the supply of the hamlet in question would lower assuming they win the battle.
- For the army arc, this could incentivize the use of mercenaries since they self-supply their own equipment and repeated successful pillages of a site would mean that not enough armor and weapons if nessecary can be produced to supply every soldier who might join the entity's state army shrinking their potential numbers and strength.
- Continued elaboration on the economy arc, and the current villian arc, the disrupted economy attracts merchants who will attempt to sell their wares to a besieged neutral, allied or home civ, increasing their supply by a small fraction in return for increasing their personal accounts, and villian networks can altruistically buy supplies in order to secure influence and trust with certain figures.
Other W.G effects may include more realistic depictions of a heavily hit town in a state of war besides depopulation of the defending citizens, starvation, shops with very few wares, and thin animals. For players in fortress mode, besieged factions may have less goods, but have better export prices allowing you to profiteer off their misfortune if not fufilling to (army arc in mind) march a army to counteract the attacks on them and be a supportive ally for some good relations.