The race you're trying to get an alliance with also has to have the Alliances technology researched...
Wauke
Stealing a quote from Kryo, since he said it better than me: Go to My Documents\My Games\GC2TwilightArnor, open the file prefs.ini, and make the following changes: Change DisplayWidth=1024 DisplayHeight=768 ColorDepth=32 Fullscreen=1 To DisplayWidth=(Your desktop width) DisplayHeight=(Your desktop height) ColorDepth=32 Fullscreen=0 Then save the file and start the game.
There's another way also, I had the same problem (with 2 screens). It's based on this: Current Display Mode: 1680 x 1050 (32 bit) (60Hz) There's a text file in your TA/DA folders, can't remember the name, it's the settings file. All you have to do is change the resolution in that file to 1680 x 1050 (I think it defaults to 1024 x 768), and the game will launch fine with 2 screens on. This applies to both TA and DA installs, I just installed the full game + 2 expans