An image from a video broadcast by North Korea's KRT on May 15 showed leader Kim Jong Un at what was said to be a missile test site at an undisclosed location. KRT via AP Video North Korea's latest round of missile tests has shocked even the more bullish experts on the Kim regime's nuclear and ballistic missile programs, who place it a few months from testing a weapon that could put a nuclear warhead on Washington. But now more than ever, the US must show resolve and not cave into nuclear blackmail, experts say.

Mike Elleman, the senior fellow for missile defense at the International Institute for Strategic Studies, told Business Insider that a recent North Korean missile launch featured a new rocket engine that improved on the earlier Musudan design that had failed multiple times.

"If that's indeed the case, and I have no reason to believe it's not, an intercontinental ballistic missile test could happen this year," Elleman said.

But although North Korea could be a few steps from testing such a missile, it has repeatedly offered to curb its tests for a seemingly small concession from the US.

Every year, the US holds joint military drills with South Korea. Every year, they get a bit bigger, and every year, they spook North Korean leader Kim Jong Un.

North Korea, through Chinese diplomats, has repeatedly floated the idea of curbing its nuclear and missile-testing programs if the US stopped the frightening exercises.

According to Yun Sun, a senior associate at the Stimson Center, while the North Koreans have a point — the US acted aggressively toward them during the Korean War, and military exercises have in the past become military conflicts — the US can't cave in to being blackmailed by North Korea.

One reason the US can't make this trade is international law.

"What we're doing in terms of our defense cooperation with South Korea is in no way comparable to the blatant disregard that North Korea has shown with respect to international law and international concerns repeatedly about its nuclear weapons program," Mark Toner, the acting State Department spokesman, said in March.

South Korean marines participate in a joint landing operation drill with the US on March 30. REUTERS/Kim Hong-Ji

Simply put, the US's military drills are legal, and North Korea's nuclear testing is not. The UN has resolutions against North Korea — the only country to test nuclear devices in the 21st century — while military exercises take place all over the world without incident, for the most part.

But despite the illegal nature of its response, North Korea has legitimate security concerns. South Korean, Japanese, US, and even Chinese forces have likely thought about removing the Kim regime before.

According to Sun, it isn't just a legal matter keeping the US from folding to North Korea.

"This is a matter of principles, and should we be blackmailed out of it?" Sun said.

If the US dropped its legal military exercises to please the Kim regime, then "what if tomorrow North Korea says, 'We don't like South Korea's political system,' or 'We don't like the Republic of Korea-US military alliance'?" Sun said.

If North Korea shows that developing nukes will cause the US to cave, would other nations try it as well? KCNA/via REUTERS

"It's a matter of whether you want to create a precedent where North Korea can blackmail us to stop doing what we believe is right," Sun said. "If the US is seen as being blackmailed by a rogue state out of something we've been doing for decades, it will create questions, and once that cycle starts, there's no end to it."

Although the US committed atrocities against North Koreans during the Korean War, that doesn't grant North Korea the legitimacy to develop nuclear weapons, Sun said.

While the US and North Korea differ on the issue of human rights and forms of government, the world can stand behind the issue of nuclear nonproliferation, experts say. If North Korea developed nukes, then what would stop South Korea or Japan from doing the same?

On this issue, experts speak with near unanimity: A more nuclearized world is a less safe one.