@AlphaKappa:
I would imagine that surrounding and then converging upon an enemy territory would be more effective than a frontal assault in a lot of cases, but perhaps that’s “below” the scope of the game. What are your thoughts on the subject? Would a “Flanking” (or whatever you might call it) bonus be too much?
On the strategic scale, I think the concept would only be valid if you had a deep salient in the front line (one or more territories in size) and if it was clear that the armies in the salient were being supplied and supported by the territories behind them. In such a case, cutting off the salient would plausibly have an effect on the troops in the salient. But it’s only on the Russian front that there’s enough room for such a situation to develop, and I agree with the above comments that it’s an unlikely situation. It wouldn’t apply in the Pacific, since the concept of front lines doesn’t apply in naval warfare as much as it does in land warfare. (For example, the Japanese used submarines to reinforce some island garrisons which became too hazardous to resupply with surface ships as American air coverage gradually extended its reach.)