AI civilisations don't know when to sue for peace, or agree to a reasonable offer, as a result wars frequently take too long to be fun. In my last two games I have had two three hour wars, with all but one of the AI civilisations fighting me hopelessly outdated. Yet they still persisted in their wars, even when I was killing their spearmen with my infantry. To be fair to the AI they did declare on me just after the Aztecs did. The remaining AI was a little behind me in technology but outnumbered me several times over, but attacked in small numbers, allowing my cannons to weaken him and counter attacks with cavalry to mop him up. Rinse and repeat, many many times. Even when he had nothing to attack with he was still refusing reasonable peace offers. Now combat in Civ5 is FUN. But wars that last hours are very tedious. And something should be done to shorten the wars. For example, 1. Make the AI able to recognise when a war is not going well, and offer / agree to a peace treaty. 2. Make the combat AI more effective by taking the precautions a human player would take, such as guarding bombard units with melee units, not leading with bombard units, and attacking with sufficient force to get the job done. 3. Bring back war weariness. Simple to implement, and naturally limits wars to a reasonable time.