When you get attacked by two armies at the same time all kind of weird things happen.

- The game tries to resolve the battles at the same time. So you get two battle start dialogs, followed by two separate battles;

- Sometimes the armies get split up or moved to another tile. So the first battle your complete army fights, but the second battle, only one unit of the army has to fight. After the battle the remaining units are on a different tile;

- When two armies attack a city, you can loose the city, even when both battles are won, just because your army gets split up or moved.