Advanced Diplomacy- breaking alliance, declaring war?

why would you want to do either of those? alliances are usefell and why give your future slaves a chance to prepare before you asault their systems?

To break an alliance go to the Foreign Relations Tab. There should be a box when you click your ally that says something like "Break Alliance". You can not break Alliances with Minor Races without refusing help.

Theres no "box" to declare war against any enemy. There are other ways than to "sneak attack." You can ask for outrageous demands so your relations will go way down and they'll eventually declare war with you. Another way is to put transport ships in their area of influence. All Civs hate this even if you are not even going after them. Also, spamming influence (maybe military) starbases around their planets. Eventually, they'll get fed up and declare war. But, these are examples how you can make the AI declare war on you. The only way you can declare war on another Civ is to attack them.