We had a huge technological advantage over the Aztecs, so any of our units is more than twice as strong as theirs. I also sold them the useless music tech for all their gold to avoid them from upgrading their bows to muskets. The Win/lose ratio of the last turn set is 88/11 which is mainly due to the obsolete units the Aztecs had (I was mostly on the offensive side) I see war declaration as a 3 steps process: 1. A surprise attack on the first turn to gain as much as possible (resources, workers, units in the field and of course - cities). In the first turn I took Atzcapotzalco that was in reach of our cavalry. That cities was defended by only 2 bows and the culture bonus was 40% which gave us almost 100% chance of taking in on the first turn with the four cavalries that I got their (only two were needed). In the first Arab war I took 2 of their cities on the first turn that was next to our borders. 2. the second step is to handle the counter attack. In the case of the Aztecs it was with obsolete forces which made it short and easy. both the Arabs in their time and the Chinese send modern units which caused some casualties. 3. the third step is to march to their backyard and take off their cities. after the counter attack is over the AI will garrison most of his units in cities. you just have to march on with cats/cannons/artilleries and take them. usually this is done one city at a time, but the Aztecs were so backward.