The North Koreans are not undermining to dispatch missiles conveying warheads of any sort at Guam. They are discussing a rocket test, where the missiles would arrive in the Pacific Ocean close Guam. This would be another infringement of the UN Security Council Resolution which says that North Korea should quit testing missiles. It would be an intense infringement, in light of the fact that the missiles would need to fly over Japan to achieve Guam.
Guam is an unincorporated United States territory in the western Pacific Ocean. the population of Guam is nearly 160,000 . Guamanians are American citizens by birth.
It would not be an “attack” in the typical importance of that term. The US would not reaction by dropping atomic bombs on North Korea. The US may assault the North Korean dispatch locales with journey missiles conveying traditional explosives. The US or Japan may attempt to shoot at the North Korean missiles noticeable all around.
What the North Koreans truly need is for the US to scratch off the joint US-South Korean military activities which are booked for in the not so distant future. That is not going to happen.