Actually, DAT's post was spot on. No nation would send their troops into the US to patrol. We're too armed, there's too many of us, and we're better at organizing than people like the Somalis, especially in terms of politics and love for region/state. The only way it would make sense is for American troops to don the blue berets, but even that wouldn't happen as the Constitution prohibits it and polls have consistently shown American GI's, by a majority, will not turn their weapons on their fellow citizens. If there's ever societal breakdown, troops will simply head back to their states to protect their families and you'll see militias popping up to protect the local municipalities and states. ...and no f'n UN goon is stupid enough to venture into that situation because it would make Somalia look like a day at Disneyland.
BTW, both DAT and myself are military veterans. DAT is a, IIRC, soon to be retired field-grade officer and I'm a former NCO.