At one point in Beta I or II there were three different empires named "Syndicate".

Allowing multiple empires to have the same name could cause all sorts of confusion and potentially lead to exploits. For example, since attack messages only give the name of the attacking empire and don't, e.g., highlight their territory, an unscrupulous player could try to trigger war between two other players by creating a new empire with the same name as an established player and launching an attack in the hope that the wrong player will be counterattacked.

Dead empires' names should probably also be reserved on a per-game basis so that they can't be "brought back".