There are certain rules and community guidelines that must be adhered to when creating a Player Name in Medieval Empires. 

• Player Names must be limited to 21 characters
• Player Names cannot contain any offensive words
• Player Names cannot be those forbidden in one or more countries (eg. "Adolf Hitler")
• Player Names cannot use words like 'Moderator', 'Administrator etc that signifiy an official position
• Player Names with invalid characters (!@#$%^&*()...) are not allowed
• No blank spaces at the start or end of the Player Name
• No consecutive multiple spaces in the name - they will automatically be merged into a single space

Make sure that the Player Name you choose abides by these guidelines - Happy Playing! :)