Why am I never attacked? Why is the AI so peaceful?

I usually play prince and I usually win the games. What I hardly get ever attacked. Sometimes not even until the modern era. Is there a tweak or a mod to change this?

Or should I declare a war in the beginning of the game so that the game gets more interesting? Usually, I don't see a reason for doing this.

AI gets more bonuses as you increase the difficulty, prince level is the "normal balanced" difficulty. I suggest you try harder levels for more aggression.

Since after prince, at king AI gets tech, unit cost, unit amount, growth rate etc bonuses, they are more likely to grow a military faster than you and attack early.

In prince mode, since everything is equal, the human player usually has at least equal power with the AI nations. This discourages them from attacking, AI doesn't like to enter a war they cannot win.

Here check the differences:

http://www.civfanatics.com/civ5/difficulties

Check your demographics screen - If your military is higher than anyone around you, they're highly unlikely to attack you. You can still piss them off enough to make them try.