We nearly had a war in 1994, which forced the United States to negotiate directly with North Korea.
We had the Framework Agreement in 1994, which froze their plutonium reactor, kept it frozen for eight years. That was a great success, but the U.S. didn't hold up its side of the bargain to go ahead and normalize relations with North Korea, to provide light-water reactors as a substitute for the plutonium reactors, and eventually the North Koreans decided that we weren’t upholding the agreement, and they started their second enriched uranium program.
It’s important to understand that North Korea is a garrison state with a million men under arms. It has another several million who have served for long periods of time in the military. It’s been sanctioned since 1950, when the Korean War began.
It’s been isolated by the United States since the regime was formed in 1948. They are used to outside pressure. They’ve lived with it. And they continue to live with it.