In Gordon R. Dickson’s book Way of the Pilgrim, the Aalaag conquer the Earth. The Aalaag have better weapons and armor than humans. I wanted to have a fantasy setting with that same feel. The Assyrians were a powerful Bronze Age empire known for their military capabilities and cruelties.
I used these ideas as I designed the World of Tiglath. The differences affect every part of life. For example, the standard flint and steel that most characters have does not exist. Starting a fire is much harder. Non-player characters will always have someone responsible for maintaining the hearth and keeping the home fires burning because if the fire goes out it is not a simple matter to restart it.
Paper does not exist. Writing is done using a stylus onto either wax or clay tablets. Wax is cheap and can easily be erased, changed, repurposed, or destroyed. Clay tablets dry quickly but become permanent. Firing the clay turns the tablet into ceramic.
Saddles do not exist. Carts and chariots are used. All of these things significantly change the way the fantasy campaign feels. Because this setting is semi-historical there are lots of resources available for research.