Go to "Diplomacy", turn your own relation to peace and wait till the AI agrees.
Depending on how many units and provinces an AI has lost, it may take several hours to several days.
Browser games are an ingenious business idea to lure out money -
- more or less cleverly camouflaged as a real game sometimes.
So beware of caltrops, spring-guns and booby traps.
Warning! Texts above this signature may contain traces of irony!