Chosin next steps
It would require a couple key modifications. Let's try to detail these out one at a time.
1. The Order Deck
In The Chosin Few, the Order Deck is small and specific. Three cards that always show up in exactly the same order. This works well for a single battle because it allowed me to control the story told through the mechanic. I'm not sure it will work as well to have a static structured set of orders for a larger war with numerous battles. Ideally, I think I would want to come up with a way of giving the player their orders as relative to the current war situation.
For example, instead of having an order call for the player to take and hold a specific location, it would call for them to take and hold spaces of a category. Like a resource or enemy facility.
The other thing that Order cards do is tell you where enemies will be coming from in the form of Lines of Departure. I may want to separate that function out to a different deck. An Enemy Operations Deck... Which could also manipulate what kind of arrows they follow perhaps...
2. Activity Deck
The Chosin Few Activity cards always have 3 points that new enemies will come into play at, and two colors that will move and 1 card is drawn per turn. For a larger war, I think I would design the cards to have one or two enemies come into play per card with only one color moving, but I would have the number of cards drawn per turn varying based on the current enemy operation(s) in effect.
3. Loss Conditions
The loss conditions for The Chosin Few are all based on the idea of not escaping. For a full war that the loss condition is more likely to be about losing ground or resources.
4. Strength Tracking
In The Chosin Few, the player only has two units so it made sense to track each one's strength to a fairly granular level. But in a full war, the player may have numerous units to keep track of and each one having its own track would likely be cumbersome for the player. This will likely require a new combat system. It should be just as simple.
What I'm currently thinking is that I will add a conflict resolution phase. During that phase if any enemy units are in the same space as your units a battle happens. Some kind of roll will happen and units will be removed from either side as appropriate. Units that are in the same space as enemy units would be unable to move away until it is cleared of enemies. I think this will lead to a good simulation of front lines. But of course, it needs to be tested. For the roll, I'm currently thinking it should be a success system with loads of dice scenario. So for a starting point, for each unit in a contested space, roll one dice. Each 5 or 6 removes a unit of the opposing side.
In any case... it's a starting point.
5. Resource Management
It would be nice for a larger war if taking (or losing) certain territory had lasting gameplay effects. Maybe certain actions require oil so if you have no oil fields you can't take those actions. Or you can't launch planes if you don't control an airstrip. That kind of thing.
6. Politics or Public Opinion
Depending on the war, this can get complicated. Say it was Viet Nam as the United States. Public opinion would be crucial to winning. Possibly more so than the actual battles. But if it were WW2 as the Germans, the larger concern might be global politics. Trying to delay other countries entering as much as possible or get as much done as you can before they inevitably get involved.
For a WW2 scenario, this could easily play into how many Activity cards you draw each turn as each new opponent would give them an additional card draw to represent their added resources.