OK, I have said this elsewhere, but will repeat it here.
In order to claim territory outside your borders you should have to do the following:
1) Build an outpost, fort or airfield outside your borders.
2) You must man it with units.
3) The more units you place in these terrain improvements, the greater the radius around the improvement that you can claim.
4) The other limiting factor is your culture. The greater your culture, the greater the maximum radius of the 'border' can be.
5) Culture also determines the maximum distance from your own national border that you can 'annex' territory.
6) Terrain improvements and units outside your borders should also carry a slightly higher maintainance cost-tying the ability to annex territory to both your cultural, economic AND military strength.
7) If another nations cultural border overlaps the land you annex, the territory becomes 'contested'. Contested territory can be given up or regained in diplomatic agreements, or by eliminating one of the causes of the conflict (the city or the tile improvement).
8) Once a city's culture reaches a certain threshold, though, it should be able to overcome a tiles 'contested' status-thus giving final primacy to culture over military superiority.
Hmmm, whilst on the subject of forts, etc, does anyone else think it a bit strange the number of units which can fit in a single city? I mean, Adelaide is probably the equivalent of a size 3-4 city in Civ3 terms, yet I'd be lucky to find the equivalent of even a UNITS worth of infantry here-and we even have a BARRACKS!! I understand that realism doesn't have to be absolute-but I do feel that there should be a much greater relationship between a city's size (population) and the number of units it can have fortified there-more if you have barracks or other similar improvements. In addition, the TYPE of unit should have an impact on a city's happiness if it is fortified there-so that militia or reservists (National Guard) might have much LESS impact than tanks and nuclear missiles. Other units needed for the defense of the city would either have to be raised as needed from the civilian population and/or stored in forts and other structures within range of the city. Although it might sound like this gives an advantage to the attacker, I am Praying that an
'all move' ---> 'simultaneous attack' system will be implemented which would allow you to bring in units from nearby forts, in order to protect a city which is about to come under attack, without the need to fortify them there long-term! The up-side of this is that we would see more wars fought on 'battlefields', rather than inside cities which, lets face it, is a mostly 'MODERN' phenomenon!
Yours,
Aussie_Lurker.