To build on Lazs and Rude ...
Instead of having what we have now with a "zone" base, move that notion to the "Capitol".
Each one of these "Capitols" will supply a certain amount of airfields that surround the "Capitol".
I don't know what the total amount of fields that are allowed on a big map, but lets say there are 240 total fields/VHs ... that would be 80 per country, so if a country has 5 "Capitol"s, thats 16 fields attached to each "Capitol".
With that, also move the "score-whoring" strats (ack/fuel/troops/etc) within and scattered about the "Capitol" area, so as the bombers come thru, they can weaken the supplies as we now have, along with trying to level the "Capitol". These supplhy strats WOULD NOT be identifyable with big shining icons, you have to find them and remember their position.
Now, each field is still capturable and if all 16 fields are captured, the "Capitol" is turned over to the country that owns all 16 fields.
The "Capitol" itself is capturable, and if you capture the "Capitol", you automatically take the 16 fields attached.
Taking a "Capitol" will be no easy task. Lots, and lots of ack and the closest bases are no more than 1/2 or 3/4 of a sector away.
To capture a "Capitol", you must land 30 troops at one or all of the 3 map rooms that are within the "Capitol" city limits. This necessitates the need for some serious organized destruction and capping to take a "Capitol".
The war is won when one country has no more "Capitols".
Fuel NEVER gets below 50%.
Rebuilding of the structures within the "Capitol" area (ack/buildings) are done by AI supply only. Strat targets (ack/fuel/troops) can be resupplied.