Hi Mongol
I tried to figure out how the remove the forces worked. (For C3C, but I guess its the same for all versions)
This is what I come up with:
Each turn there are increase in points for each unit in enemy boarder.
Base value : 128
Multiply by :
1/8 for none attacker
1/4 for units on water
2 for units on land next to city
The enemy can force you out when 512 points are accumuated, then the points are reset. If, on the other hand, you deside to leave voluntary. The points will be halved for each turn.
Ex:
A warrior can be thrown out after 4 turns, or 2 if next to city.
For a worker or scout the number of turns are 32 or 16.
A boat loaded with 1 unit can be forced to leave after 8 turns.