What should the world do about North Korea?

North Korea has been a threat to its own people, its neighbors and to the whole world for decades. But recently, they are becoming more and more aggressive by testing long range missiles that can carry a nuclear warhead and hit Los Angelos, California in 30 minutes.
Yesterday, American Otto Warmbier died. He had been held by North Korea in a brutal prison and sentenced to 15 years of hard labor for "propaganda." Otto's health deteriated rapidly and the U.S. government was able to secure his release last week. North Korea claims he was suffering from food poisoning, but the U.S. doctors said that is not true at all. Poison is a likely source. He had severe brain damage and was mostly unconscious. He parents broke the sad news yesterday that he had passed. Otto pictured below.

What should the world do about the escalating behavior of Kim Jong Un? President Trump strongly condemned what happened to Otto. The U.S. has 50,000 troops on the North and South Korea border. And China, who sits on the North border, has had enough of this behavior too. Is it time to do a preemptive strike and take out their nuclear and missile capabilities? An all out war would be disastrous for everyone. Millions would die on the peninsula and millions more refugees would flood to China. Maybe former NBA star Dennis Rodman has the answers?
As dumb as that sounds, he was just there a few days ago and met with the crazy leader. One thing is for sure, the world can not sit around and wait for Kim Jong Un to fire a nuclear missile at Japan or the U.S. I think it is time to strongly consider setting their military back for 20-30 years. Let me know what you think. Cheers!