Movement zero.
This way you can place where you want and reinforce it.
Trenches would be destroyed and damaged by artillery range 2 and 3 hexes
the a player can attack weak trenches to gain ground.
Each level could represent
1 basic depth
2 deep depth
3 with fortification
4 with machine gun nest
Or some other historical simulation
I think country moral would have to be in the game. After all the amount of men lost on the front effected moral and the will to surrender.
The most important thing would be to find the key to make it fun and not boring.
Static lines seem very boring. There was movement in the war, but there must be other things for players to be challenged and objectives to seek.
Spy's that can effect moral when key members in Politics get killed.
ORIGINAL: gwgardner
One restriction in ToF is player-built fortifications. In a WWI game, you would have to allow for dynamic player creation of trenches and fortifications, AND you would have to do it in such a way as to recreate that difference between western and eastern fronts that you mentioned.
In other words, you would have to have the proper game mechanics that would allow a player to build trenches/fortifications, but also to recreate the conditions/tactics whereby that trench mechanism would not everywhere on the map be the best thing for a player to do.
I hope I have been somewhat clear.