Click on the burning paper icon under the text area to break a treaty, repeat this until you're at war.
Note that this icon (available in the diplomacy window if not at war) forces a reducton in treaty (at the cost of reputation).
The red scoll above the text window can also be used, but only if the opponent agrees (AI will never agree, as far as I know)
Posted 13-Sep-08 20:32 by Retudin