I don't know where you live, but where I do, unwelcomed troops are referred to as "an invasion force."
Where I live, a platoon of Australian soldiers paddling toward the SuperDome after a natural disaster to rescue their countrymen, while locals and the NG sit on their helmets, would not be considered an "overt act of war." However, I must admit, where we live, many people have common sense enough to not exaggerate to make their simple point. And they are honest enough to admit it, when they do.