Thanks for the reply!
No, most treaties are meant to remain active for the duration listed, and you don't have the option of cancelling them early. There was a bug floating around where you'd receive word that the computer had decided to cancel its treaty with you but hadn't actually done so, so this may be what you're experiencing.
Oh they are definitely cancelling my trade, economic, and technology agreements and our non-aggression pact. Then two turns later they declare war on me. Doesn't seem right that they can do this to me but I can't do the same back to them... This is after having friendly relations. Ticks me off. 
You can look up (or modify) the duration of various treaties in the Treaties.XML file located in \FE Legendary Heroes\data\English in whatever location you have Steam installing games. Alliances are supposed to last 99 turns, Tribute is supposed to last 30 turns, and Non-Aggression Pacts are supposed to last 50 turns. Economic Treaties (which creates a trade route between your capitol and theirs), Peace Treaties, and Surrenders are instantaneous treaties (0 duration), while Trade Treaties (which grant a 10% income bonus to each party) and Technology Treaties have indefinite durations.
Thanks for the explanation. I'm going to hold off modding the game before I get a good feel for the vanilla version. I just want equal treatment. When I'm playing all nice nice and they take my money and make agreements but then soon after reneg on it all but I can't do the same makes me say things to my computer. My wife laughs from the other room. I like playing with conquest only rules so having the remaining people be close and friendly to me and there's nothing I can do to piss them off kind of stinks. Taking the ability to break my agreements with them only adds to it. With some AI I've rarely gotten to 50 turns for the non-aggression pacts... I'll have to start keeping track of who does what to me to see if there's a pattern. At first I thought it was the Empire folks doing it (I"m kingdom) but then the Kingdom guys started to do it... Thanks again for the reply.
