If youre lookin for a foreign enemy military, the add UN troops invited in for pacification and peacekeeping.
Bingo.
The barbarians will form "no go" enclaves and parallel societies, like the banlieues in France and certain areas in the north and midlands in Britain.
People outside the enclaves will resist the depredations of the barbarians, but the socialist government in Washington will be dependent on the support of the barbarians for their political power, and will identify more with trasnational socialist elites than with their own people.
The government in that situation would likely need to resort to foreign forces in order to suppress the native resistance.
Unfortunately, a lot of troops and cops will enforce Washington’s decrees, no matter how moronic. I don’t think they’d have to bring in UN blue helmets to do their dirty work. I just added them for dramatic purposes.