Politically, you have the same world issues as with an external kill zone, though without the issue of conquest of foreign soil. Domestically, you also have the Fifth Amendment taking (just a matter of writing some cheques), as well as the unpopularity with the locals whose land is seized. And, as always, the fact that there are a ****-ton of illegals and sympathizers already here who would become very agitated if their brothers and sisters start pushing up daisies as a matter of national policy.