When a declaration of friendship ends with an AI, the huge bonus to their opinion of you that comes with being a declared friend lingers for one turn afterwards. This means that as long as you renew the friendship on that turn, the AI will always accept, and will remain your friend for as long as you want. The major consequence of this is that as soon as you've made all the AIs your friend once, which is easy to do with just a gift of gold, you have total control over whether or not they're allowed to go to war with you for the rest of the game, and can abuse them for favourable deals and alliances. This breaks the game completely once you know about it. Please fix.