Diplomacy might not always work, but it should always be tried. When a nation is pursuing nuclear weapons, and you don't like it, you ask for a meeting. And, not with just diplomats, but with the big man himself.
We should have such a meeting with North Korea's Kim Jong Un. Go in, sit him down, and diplomatically tell him not to do it. Quit testing, and quit seeking such power. Reason with him. Tell him how the U.S. is no threat to him, how China and Japan and South Korea are not threats, how United Nations sanctions could hurt his country.
Reasoning does not always win, but it will never win if it is not tried.