Firaxis has assured Civilization V players that the diplomacy engine for computer controlled opponents has been improved for the Gods & Kings expansion and I might have just experienced one aspect of the upgrade in the form of a Medieval World War I.
Last time I checked in I was bringing up a lone siege engine and a mix of spearmen and archers in order to take over the Vatican city state.
Once this was accomplished, two civilizations that were close denounced me because I was an expansionistic warmonger, which I felt was a little unjust given that they also seemed keen on gobbling up city states that were close to their borders.
I then also took down Lisbon and another neutral town and that made 5 of the civs on the map declare outright war on me, with another two of them denouncing my actions.
I wasn’t truly prepared for war on multiple fronts and I thought that I would lose a few towns and then be forced to enter a humiliating peace.
Unfortunately, the improvements made to the diplomacy with Gods & Kings failed to also affect the actual tactical calculations of the Artificial Intelligence.
Despite clearly fielding more troops than me, the other civilizations failed to coordinate any sort of battle plan and actually left me alone for about 10 turns after they declared war.
After that period (check out False War for real-world similarities) they finally marshaled some pretty strong forces, with the Swedish Gustavus Adolphus very well positioned to get two of my smaller cities, while Dido had the troops to cut off my own potential reinforcements.
I was ready to get a sound beating, even if by that point I had some crossbowmen myself and a lot of pikemen in the production pipe.
As always, no plan survives contact with the enemy.