On early Tuesday morning, North Korea fired a missile over northern Japan and into the North Pacific Ocean. In multiple sources, this missile test has been described as a huge "unprecedented, serious and grave threat" to Japan.
Previously, North Korea have only fired projectiles over Japanese territory twice and in both cases, these were said to be carrying satellites into orbit; no such claim has been made this time around.
It's easy to understand why Donald Trump and Kim Jong-un would (and have been) threatening one-another with missile strikes:
It is important to remember North Korea's attitude as well. Officially, the Korean War in the 1950's never ended. What the world has been living with is actually a 60-year ceasefire. North Korea and the United States are still technically at war with each other. Source.
What I don't understand though, is what firing missiles over (and therefore threatening) Japanese territory will achieve?