The Aztecs were a very powerful empire.But they were also very religous and that was there downfall.They believed that one day there god would return.Since they had never seen someone with different skin color they thought that they were their gods.They welcomed the Spanish in and treated them like gods.When the Aztecs found out that they weren't gods they despised each other.The Spanish didn't attack them directly.They knew they couldn't win because they only had 600 men instead they blocked off their water supply and the Aztecs fell.Plus the Spanish brought disease to the Aztecs.

Things city designers can change is how they make the streets so there won't be many car crashes.If you make a street a specific way then you have to make sure people can easily drive on it.Also you can't make a bad street in a very populated area.Plus you can't make a city where a lot of bad things happen like torrnadoes and other things