I was given the "You better give me money now and more or else" from my opponent. I figured that I would accept it knowing that I probably will break it shortly after.  I could not find a way to either declare war on this opponent or discontinue the payment.  I feel that in the action column in the city enchantment window would be a great place to discontinue the tribute.  The row is already there. All that is needed is a button.  I am also not sure why I could not declare war on someone that forces me to pay them.

On a side note this brings up another issue.  There are a lot of tool tips in this game, which is great, but a lot of them are hidden unless you know to roll over these areas.  I would find this, as a new user frustrating.  Example is this forced payment text eluded to the fact that I would be paying more after my tribute but does not say how much.  I think a simple 10% of future income should have been added right to the text and be done with it.  To have to hunt for this information in a tool tip can be tedious.  Another example of hidden elements is the city enchantment window.  I always forget how to get to this window and have to hunt for it.  Lucky for me, I know it is there so I just hunt for it.  I believe a new user will take a long time to realize where to find it.  It is an important window so some icon or something that gives someone a clue to pick it for this information would be nice.