After the alarm and confusion caused by the explosions at the Boston, everything became clear when Kim Jong Un, Supreme Leader of North Korea, sent a press release claiming that this was 'only the beginning' of the 'sacred war of justice.'
"You see," the release read, "All the able bodied of America will soon be destroyed, and no one will be left to fight us but your lazy, sluggish obese."
After googling 'american army,' Kim Jong Un was impressed by the muscular, macho men portrayed in the first search result, the video game, "America's Army." He now plans to attack gyms, sporting events, and all restaurants that are not McDonalds.
The US government is currently in the awkward process of discouraging people from entering gyms and exercising in public.