I think the founder of a city should be able to influence the length and intensity of the resistence. If I take New York from the Americans, Roosevelt should be able to spend money to make the resistance last longer, keeping me from using the city and possibly damaging my troops in it. If we make peace, one of the possible conditions should be using his influence to shorten and minimize the resistence.
Also, more than one side should be able to give something up in ceasefire negotiations. Not all wars are one-sided routs. Well, all of mine are, but I only play at Prince.