The Game Table is a world of chaos. Each time that a new one is created things are changed so that it is never compleetly the same as the real world. Some times it is somthing simple such as Orcs and humans switching roles with the Humans becoming savage powerfull beasts and the Orcs infinitely resourcefull and Proud beings.
Changes could be as subtle as Yes meaning No in every language or as vast as magic being the subject of what is knwon as Magic Engines. Without one of these things magic dose not work further than cantrips. With it a trained person can do great things. But that is not important .
These things are built to make the world a very alien and diffrent place from that of the real world or that world that the characters are used to . I would imagine the best Idea would be to not inform the PCs of the changes to the world to build on that atmosphere of chaos and the feeling that nothing is what It should be. That paranoia about everything being diffrent.
Over all the players should be in a bit of dissarray untill the campaign is comming to a close. A constant threat should always be their doing something that is normal to them that causes a large problem in the game table…