In Civilization, how does the AI act, depending on each difficulty? Is there a special way they do things?

I’m a new player at Civilization 3, and I want to know how the other countries/civilizations will act. Is there a reason they will move the way they do? Is there any special thing to watch out for? How does the AI change when you select different difficulties? There should be a certain way that you will be able to react the the AI so you can get better games? Depending on the difficulty, will the game last a bit less, because it’s more difficult to stay alive?

Thanks in advance.