We can now say with confidence that the undead menace has arrived. Despite all signs having been to the contrary, we now know there are zombies in every nation.
Whether because zombies are slow moving or because of someone's tardiness, not all nations were aware of zombies at the same time. Nations exploring their options before the appearance of zombies would have been unable to elect to build a zombie empire, and any selection they made before the appearance of the stumbling dead within their borders has been reset.
If you wish to cure or exterminate your zombies, double check that your selection is active!
Further information will be provided as we can.
The parable of the zombie and the hare comes to mind.