Soldiers on any type of campaign should also have to deal with some sort of supply line. Many of history's successes, defeats, and standstills have been due to inadequete supplies. Operation Overlord was an example of a success for supply lines, while the invasion of Russia (either 1812 or 1941) was a main example of supply lines being drawn out too far to handle. The Allies could have reached Berlin in WWII by 1945 if fuel had been allocated to Patton's drive into Germany instead of Montgomery's Operation Market Garden. In C3C, you shouldn't be able to plown across a continent of forests in a campaign of war without having to keep up with food and ammo for soldiers and fuel for tanks. The same goes for naval vessels; you shouldn't be able to send a submarine out to sea and never have it return as it sinks half a fleet in the middle of an ocean. Hopefully this will at least make it into Civ4.