Dark Sun Warriors

In my created universe "Storm of the World" here is some ideas that came to me in the middle of the night.

The dark sun warriors wear a blend of desert brown ponchos and high tech white metal. Also the smoke stacks and exhaust pipes are prominent in their outfits as well as their buildings. Mad max meets metal gear.

The wall around the citystates have massive canons with 2 barrels sticking out . The walls are a thick curvish future concrete wall.

The "blue knights" are like the templar knights and have worked out agreements with the city states where they provide some of their technology and the blue knights are given a base in each city state and funding to continue to protect people and escort people out in the wilderness.
They also have way stations on roads between cities that they man and protect.

The event that caused the dark times and the rise of the city states I am going to call "the Fall"  Basically its the fall of the Roman Empire that lead to medieval society. So in my world the event that took back the earth and caused the people to come together in the city castles is "the Fall." Probably would help if I figured out what that is exactly.