AI doesn't normally lift trade embargoes and when they do it takes quite a while for it to happen. If you do things right however they won't impose one on you in the first place. When playing against the AI, especially the Elite AI, you have to remember your diplomacy and what's going on with the countries around you or you can wake up one day and find that half of the freaking map is now at war with you!
When you get ready ready to attack a country you should first place a trade embargo on who you are going to attack, then give it a few hours, officially declare war against that country and then attack them in that order. If you go in there without notice and attack and that country happens to be allies with others they will go to war with you as well in defense. You should check the newspaper first for most popular and most dreaded nations. If you attack a popular nation without warning you will end up at war with multiple countries. If you attack a most dreaded nation and do it properly you will pick up allies. Always pay attention to what the newspaper is telling you.
You never know how the other countries are going to react to what you are doing so try not to be at war with too many at once or you could end up in trouble if you piss others off with your actions.
