I understand that this captures one's attention,...but read the announcement critically. It welcomes the "PARTICIPATION" of these countries. The description of the event makes it clear that the focus is on attempting to prevent some unknown persons from entering into the U.S. to carry out an attack. Well, that makes Mexico's and Canada's participation rather obvious, and they could participate easilly from their side of the border, simply attempting to cooperate in the prevention of anyone crossing the border.

The confusing bit, however, is Australia and Britain. The only logical explaination for their participation (that I am aware of) is that they have had an intel-sharing agreement with the U.S. for a long time, providing the FedGov with physical & signals surveilence on U.S. citizens that the FBI & CIA are prohibited from acquiring on citizens, and vice-versa.

But nothing in the announcement gives sufficient reason to believe that uniformed soldiers of other nations will be operating on U.S. soil.

(However, I am as aware as you are that our masters are fully capable of trying such a stunt.)