The posse commitatus law lapsed during the Bush administration, if I understand correctly. We were not allowed to use Umited States troops against United States citizens, in part as a reaction to some of the events around the civil war.
This law, as I understand it, allows us to get around the law, now lapsed, in an even more direct fashion, by using Canadian troops.
I am somewhat hazy about all this, so I urge anybody interested to do their own research. I believe it's part of the attack on civil liberties and civil protections against government incursions against the population by the government over the past 30 or 40 years.
I really would rather that everybody simply take me as a nut-case on this, however, and do their own research to confirm or disconfirm my conjectures. I would frankly rather be completely wrong about this in every particular than be right in the least.