It's really a geopolitical theory of territorial defense against the system's 'need' to regularly devalorise overaccumulated capital. Harvey's book Spaces of Capital gives you all the details, so the 'functionalism' is put into context of a rich poli-econ tradition. It simply builds upon Marx, in what I think is the proper spirit, accepting class struggle, contradiction, contingencies - but still insisting on the underlying dynamic towards overaccumulation and crisis formation. When crisis displacement no longer works, as appears to be the case now, watch out for that nasty devalorisation, and the ongoing struggle over who will bear the brunt of it.
And I agree with you about the danger of fascist movements. Glad y'all are ridiculing Rush these days...