[MaxWilson]

I should also note that you *have* to have tactical superiority. You need to feel confident of defeating any one of his armies in a straight-up battle with PD on his side. If you can't smash any army he parks on your border, he can keep building up troops along your border, and your defending army is pinned (since you don't have the one turn's warning of him moving an army onto your border). And if you're that weak, you'll probably have to keep pouring reinforcements onto your border to match his buildups, and playing the Maginot Line game with a richer enemy is a lost cause. So you *must* have tactical superiority for the chokepoint strategy to work, and if you don't then you must either expand or research until you have it, while your defending armies buy time by dying bravely.

-Max