[throw_pm23]

There is a trivial alternative that military strategists have been suggesting for decades. For a nation of 20+ M, having a reservist army of 1M would be feasible and make the island impossible to invade even if the rest of Earth would join forces to do that.

[Epa095]

Oh? The army still needs resupply, and the population needs food? Seems like a siege of an island is pretty easy.