Okay, maybe I can combine Jeremy's and HG's questions in a discussion of
the "center". Certainly, control of the center is very important in these
sorts of games, or in most actual battles, for that matter. But "the
center" is a somewhat nebulous concept when expanded from FIDE to
Chieftain and Warlord. On a 12x16 board, the "center" is a 4x8 strip
containing 32 squares. Much easier for both sides to get into in force, and
far harder to control. On the Border war scale of 16x24, the "center is
going to be around 6x12, 72 positions to control. And the "edges" are 6
squares deep. 

At the larger sizes, control of the center often means the opponent's army
is broken. But there is no first move advantage to controlling the center,
because the board is so large, maneuvering around in it a square or two
closer to one side or the other - consider the logistics of invading the
opponent's home territory, where the army and command structure are
initially established. It takes time to gather the troops and press
forward. 

However, no static defense has seemed to work. It's always been the case
that if a player cedes the initiative, the other player can pick a spot to
attack where the attacker can guarantee overwhelming force. It is annoying
that so many of the games on Courier are gone or inaccessible, but please
look at the 2 games of Warlord being played now to get a little idea of the
flexibility of the games, and why I say the first turn advantage has to be
washed completely away at some point.

The Border War playtest I ran Thursday night allowed promotion, but neither
player bothered. Even with 12 moves/turn [48 piece armies at start,] it
wasn't worth it to send some units off to try to fight their way through
the opponent to promote. Although there were 4 geographic targets - towns -
in the center of the board, so that made it less worthwhile to bother with
promotion, because victory was to the player who could occupy 3 of those 4
towns at the beginning of that player's turn. 

I think that the center of the board geographical objectives would have to
give the same effect as promotion, and they aren't all the way across the
board. And I still don't see the need to say there is a first turn
advantage. It's possible there is one, but I have to say I see it as lost
in the noise. 

Just so you know, Jeremy, this series of games is also meant to show that
there can be humanly playable super-large games, boards on the order of
100x100 squares. These games are scalable. Border War at 16x24 is 4% of a
100x100 board. How many steps do you want?