Precontrolling the map

If your game is 2 armies fighting along their coterminous borders, then it makes full sense to me that the game starts with armies AT the border within striking distance of one another and I would totally agree with you that having more than just a few "neutral" cities/strategic points in-between doesn't make much sense.

I guess you could take turns at placing your armies along the border, perhaps with the FULL details of each army not revealed until a later time (perhaps at the starting whistle.) Then you still have a sort of opening game, with strategy and bluff, etc...As a kid, I always saw the opening phase of Risk as particularly interesting, full of threats, implied truces, shifting priorities, and so on. It would be a shame, maybe, not to have some kind of build-up to replace the advancing-together-phase which ought to be tense, strategic, and as much a contest of generalship as the final head-on action.

I think the way you describe your game allows for the opportunity for a number of different scenarios.

Many wargames try to recreate/simulate a previous point in history. In those situations, opposing forces are within varying degrees from one another in terms of striking distance, based on the historic scenario they're trying to emulate.

What's the case for your game? Are you trying to emulate a specific scenario? Do you want the players to think tactically since their enemies are so close to one another? Or would you prefer for the player to develop a long-play strategy, and instead leave a number of neutral territories between them?

Either choice adds or reduces game length, as well as the depth of strategy with which the players can engage. Another advantage of this kind of perspective is that your game could host a collection of pre-made scenarios, as well as guidelines for developing one's own scenarios. It increases the replayability of the game itself.

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Also, I have one point of contention with your original assumptions, but maybe this is just splitting hairs here.

I think it's important to remember that in most games, the notion of "neutral territory" indicates a rulership that's not one of the players, or a relatively uninhabited area with no ruling faction. It's understandable that a region's rulership hasn't completely allied itself with one or the other most-powerful factions (that is, the players). This justifies in some way the players indiscriminately invading and conquering the local forces.

There are few different options to delay engagement, which is really just a way of nerfing the first-mover advantage.

Chess method... no one is in striking distance on the first turn

Risk method... players watch each other set up while attacks are not allowed

Stratego method... players set up hidden from one another

Axis & Allies method... starting positions pre-baked, first turn essentially scripted.

I've seen variations on these as well. One game set in feudal Japan (forget the name) used the Risk method but also disallowed attacking certain units on the first turn. My group quickly learned that made those units effective walls in the very early game.

My suggestion would be to lay out a region similar to France and Germany. They share a nice bit of border, but there are neutral wedges at the ends.

You could actually allow several distinct types of setup. Develop one, keeping the others in mind, and only bring them in after you have a working game.

* Pre-baked deployment positions (A&A-like)
* Choice of pre-baked deployment positions (need to choose blindly, then stuck with your option even when it's revealed what the opponent picked)
* Take turns laying units in each other's view (Risk-like)
* Set up hidden from one another (requires a big, goofy privacy screen along the border)
* Bulk of units deployed to the interior, defensive units at the border (almost chess-like)

The last one seems particularly fitting if war has NOT been declared at the very start of the game. Starting the war gives a tactical advantage, but should entail some strategic disadvantage (higher cost to enter neutral territory, lower starting morale, other side gets a gift of a few volunteer militia, etc.).