The US can survive a nuclear North Korea — but a first strike could start World War III

Despite President Donald Trump's bold proclamation that a North Korean nuclear missile capable of hitting the US "won't happen," Kim Jong Un appears to be on his way — faster than many had thought — to an intercontinental ballistic missile that could flatten Washington.

But a nuclear-armed North Korea wouldn't be the end of the world, according to some senior military officials.

"We can deter them," retired Adm. Dennis Blair, the former head of US Pacific Command, said of North Korea at a National Committee for US-China Relations event. "They may be developing 10 to 15 nuclear weapons. We have 2,000. They can do a lot of damage to the US, but there won't be any North Korea left in the event of a nuclear exchange. That's not a good regime survival strategy, and even Kim Jong Un would understand that.”

The US has to live with the fact that Russia, the world's second-greatest nuclear power, openly opposes the US's foreign policy in nearly every dimension, and that Pakistan, a country rife with corruption and Islamist groups gaining traction within and around its borders, has nuclear weapons.

A senior Defense Department official with expertise in nuclear strategy told Business Insider that while the US has said it cannot and will not accept a North Korea armed with a nuclear intercontinental ballistic missile, that amounted more to an opening position in an ongoing negotiation than an intention to use military force to stop it.

"You never undermine your official position going in," the official told Business Insider. "You're never going to voluntarily back away from that. You're going to actively work to make sure they don't get" an ICBM.

"The North Koreans having nukes is a bad thing, and we don't want it," the official said. "But if we lose that one, we survive it."

Despite bluster on both sides — whether posturing that the US may attack to cripple North Korea's nuclear program or that North Korea would use its nuclear weapons on the US or allies — the defense official and other experts Business Insider contacted said they found both cases extremely unlikely and undesirable.

"But those experienced military leaders know. They've run the models. They've run the numbers," Hanham said. There's just no way to fight North Korea "without chaos and enormous death and damage to the world."

The trajectory of US nuclear ICBMs would have to fly over China and Russia — which could mistake an incoming missile as being intended for them. And while the US could use submarine-launched or air-dropped nuclear weapons, both options would most likely spread deadly fallout throughout the region that could bring about World War III — a great power war between nuclear states that the world has developed nuclear weapons to avoid.

To an extent, the US already lives with and deters a nuclear North Korea daily. Hanham said that although it hadn't been verified, North Korea most likely had a deliverable nuclear weapon that could hit the 10 million civilians in Seoul or the 25,000 permanent US troops stationed in South Korea.

So North Korea will continue on its path toward a nuclear weapon that could hit anywhere in the US — but like Russia, China, and Pakistan, it probably wouldn't use it.

Editor's note: This post has been edited to better explain how nuclear conflict in North Korea could lead to a broader conflict between great powers.