There should be a faction of aliens who came down to earth sensing its weakness and infiltrated a government through some means of possession. They would be a race with abilities similar to a better version of looted wagons except with people.

I don't think there should be any aliens.

The setting more or less keeps all factions with-in the realm of earth, with no mutants.

If there were aliens they were be so over powered, unless you did it like the Kur from Vampire Earth.
http://www.vampjac.com/vampireearth/

If aliens could travel to earth and humans can't really get past earth,it would be next to incomprehensible how much more advanced they'd be

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Penguin army: %&@# off bear cavalry

And ipod touch posting ftw

Far right winged beast of awsomeness