Nukes went 'boom', no one really knows anything except that the President was addressing a joint session of congress to discuss 'escalating' world violence against Americans. Like most Americans, the TV was on in the background letting us know that was happening, while the show's characters went about their daily lives totally ignoring what the government was doing.
There have been hints and of course speculation especially after their satellite dish caught a partial signal from Japan (although it's my partner who says Japan based on the language - he's half-japanese so it could be china or any other asian television with satellite broadcast abilities). No one there understood the language being spoken, but they did see a nice graphic behind the announcer showing a map of the US with red blinking circles around several major cities.
Also, there's a guy in town named "hawkings" that says he's a former cop from St. Louis, knows a HELL of a lot radiation poisoning, safety, and cleanup of a post-blast world. He's got a basement chock full of interesting things like a Toughbook laptop similar to the US Army field design, and a sattellite internet connection link through which he chats with a mysterious group of people. Oh, and in last week's episode, they found a man dying of radiation exposure who came from Denver with a group of 20 people. Hawkings had a VERY interesting conversation with the man just before causing his death, including word that there's a traitor in some mysterious group that Hawkings and this man belonged to...OH yes, and Hawkings is teaching his family what lies they are to tell about their past lives...and how if the truth were revealed they were all dead.