This may be hard to implement, or it may be simple. Many people seem to be opposed to server merges where one or more servers worth of players get dumped together into one land. I don't like that idea either, since it just goes completely outside of reasonable medieval events (teleports are unrealistic too, but they sure make the game fun).

Here is an idea of how two (or more) servers could eventually be joined, and it would add some additional elements to the game. For the example, I'll only discuss it as merging 2 servers, but it could potentially be scaled up.

Imagine that the two servers are separated by water, even if the water can't be visualized on the map of your home server. To explore the lands across the water, a separate tab in the "town/city/map" area could be made. Clicking on that tab would take you to the map of the next server. When you click on a location in the "overseas" map, it tells you not only travel distance, but also sailing time. Sailing time could be some multiplier factor based on how far it is to the same location on your home server. For example, if you want to attack a city that is 100 miles from your home on your own server, but you're interested in the "overseas" copy of that location, travel might be the 100 miles marching + 20% for sailing.

To make this feel more natural in a middle ages game, add some sort of seafaring research (shipbuilding, seafaring) and possibly some new classes of troops (sailor, navigator). The better your shipbuilding, the more troops that can go on an overseas mission. A higher seafaring level will cut sailing time. Place value on hero intelligence for sea captains to further decrease sailing time. This will encourage people to keep smart heroes in addition to attackers or politicians.

That sets up a situation where two servers are integrated into the same world chat. The names of the states don't have to be changed, but perhaps designating the younger server's states as "New North March" or "New Bavaria" etc. would help people know which map they are working from.

Let the two servers, separated by water, exist in a stable configuration for awhile. Players will naturally want to explore the other map, and may move to one server by choice.

When the game makers want to consolidate to a single server, let it be decided by which land has the majority of active players. Then, the system can announce (via intro or mail) that one land is dying. Have unoccupied valleys/flats begin to dry up...no longer growing above level 4. Those unoccupied lands that are above level 4 when the process begins will go to level 1 on the next server maintenance cycle, and continue cycling level 1-4. The death of a land could go in stages (first max out the valleys at level 9, then 8, etc.), all the way down to the point where unoccupied valleys/flats are only level 1 and don't ever improve. This will make that server much less appealing, and people will find ways to move their cities or alliances to the surviving map.

Once over 90% of the players (based on #of cities) live on a single map, then send another system announcement that the dying world will be lost forever after a certain time. Those few remaining cities could then be merged into vacant areas close to where they were on the dying map.

I realize this includes several changes to the game that may be too big for Age I, but I think it would make server merges something more enjoyable and a way to enrich the game.