Even if you're not a master persuader, there are multiple paths, and all of them can be greased. Some can be greased with blood and some can be greased with coin. If they want coin for peace, then they can be bought, and enough coin should ensure they stay bought. And if they don't give equitable terms for being properly bought, I'm going to have to buy their parents, their children, their extended families, and they can all rot in slavery forever! Stupid orcs.