Corrected entry: When the rest of the world finally starts seeing the lights in the sky, there is not any mention for the remainder of the movie of any military presence or actions being taken against the aliens. Given how simple the aliens are to defeat with water and physical violence this doesn't make sense, especially given the technology and weapons we have at our disposal.
jerimiah
16th Jan 2011
Correction: The reason you don't see the military attack the aliens is because they do not yet know that the aliens are hostile. It is only after the aliens land and invade the Hess' home that it is known, by which point the movie is not showing the aliens in any other part of the world.
S. Ha