What happens if North Korea gets out of hand? Here are some scenarios

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In response to North Korea's announcement that they will be deploying "small, light" nuclear strikes, the Pentagon has announced it is sending an anti-ballistic missile system to Guam. NBC's Richard Engel reports.

By M. Alex Johnson, staff writer, NBC News

While political and military analysts sound pretty confident that North Korean leader Kim Jong Un's threats are just bluster, you can't get around the fact that the region encompassing the Korean peninsula is one of the most heavily militarized places on Earth, home to three of the world's six-largest militaries.

If the unthinkable were to happen, how would it play out?

Leon Panetta, who stepped down as President Barack Obama's defense secretary in February, warned this week in an interview with CNBC that "we don't have as much insight as we should with regards to the inner workings of what happens in North Korea."

But based on declassified U.S. and U.N. assessments and independent analyses by military scholars, we can make some educated guesses:

How would North Korea attack?Probably with a massive ground assault backed by artillery fire. That's because North Korea's standing military, according to the best U.S. and U.N. intelligence assessments, is the fourth largest in the world, at 1.1 million members. South Korea's, by contrast, is about 690,000 strong.

Library of Congress Federal Research Division

That ratio — a manpower superiority of roughly 3-to-2 for the North — is remarkably consistent across calculations of the countries' weaponry, too. By about the same proportion, the North has more tanks, more artillery, more planes, more ships, more missiles. 

In a 2008 report commissioned by the U.S. Joint Chiefs of Staff, the Federal Research Division of the Library of Congress depicted North Korea as, in essence, one giant military installation:

How would South Korea respond?By being smarter and nimbler.

Much of the North's equipment is seriously outdated, going back to its alliance with the former Soviet Union during the Cold War. 

The South's weaponry is less extensive but far more advanced, thanks to modern equipment provided by the U.S. 

"Overall, South Korea's armed forces have become one of the world's more capable militaries and present a formidable forward defense against any possible attack by North Korea," the British-based International Institute for Strategic Studies concluded in 2011.

All of that presumes that North Korean troops could make it into the South in the first place. To get there, they would have to go through about 28,000 U.S. troops stationed along the Demilitarized Zone separating the two countries, supported by about 40,000 more just a short hop away in Japan and on a large military base in Guam.

Doesn't Kim have China to back him up?In theory, yes, and that's no small matter. 

China's 2.3-million-strong military is the world's biggest, outpacing the U.S.'s by almost 40 percent. In its annual report to Congress last year, the U.S. Defense Department didn't estimate how many Chinese forces might be based in North Korea, but it did outline the massive array of forces China is believed to have inside its own borders facing the Korean peninsula:

The map at left depicts China's naval buildup around the Korean peninsula. The map at right details army deployments. Click each map for its full-size version.

But it's not clear that China has the stomach for a fight. Beijing has signaled its displeasure with the North's recent provocations — just last month, it voted for a U.N. resolution to impose sanctions in response to North Korea's announcement of a nuclear test on Feb. 12.

P.J. Crowley, an assistant secretary of state during Obama's first term, told NBC News that Kim's erratic behavior has created major "frustration" in Beijing, which he said "does not want to see an implosion of North Korea."

The U.S., on the other hand, has made it clear that it will defend South Korea. To drive home the point, it sent F-22 stealth fighter jets to South Korea as part of military exercises in a show of force Sunday. And it has sent two warships to the western Pacific to watch for missiles and will soon send an advanced anti-ballistic missile system to its base on Guam, defense officials said.

Military and political analysts say China doesn't want a showdown over the Koreas because then the superpowers' nuclear arsenals become a factor. The U.S. said in an unclassified 2010 report (.pdf) that its stockpile was about 5,100 warheads — more than 20 times that of China, which the Bulletin of the Atomic Scientists estimated in 2011 at 240.

How long could South Korea hold out?Much longer than the North.

If North Korea were to employ nuclear weapons, it would impact U.S. troops and pressure Japan and South Korea to also consider obtaining nuclear weapons – something that could lead to an all-out arms race.  NBC's Andrea Mitchell reports.

To put it bluntly — as the CIA did in an economic assessment last month — North Korea is a mess internally. Industrial and power output have receded to pre-1990 levels, while frequent crop failures since a devastating famine in 1995 have compounded food shortages that have fueled chronic malnutrition. All that's keeping its people afloat are international food aid deliveries, mainly from China, which would almost certainly be disrupted or cut off in a war.

South Korea, in sharp contrast, boasts a high-tech industrialized economy — one of the 20 biggest in the world, the CIA reported. It has numerous trading partners worldwide to keep it fed and supplied. And because its communications and transportation systems are among the best in the world, it would be much better placed to coordinate civil defense and to move people and material out of harm's way.

So if a traditional assault is unwinnable, what are Kim's options?Very scary ones.

The Center for International Studies and Research, a nonpartisan French research agency, calculated in October (.pdf) that the North can deploy "a full array of what are typically described as weapons of mass destruction" — one of the biggest chemical and biological stockpiles in the world at 2,500 to 5,000 metric tons, mostly tabun (a nerve agent) and mustard gas.

In a technically secret process, South Korea is believed to have told the Organization for the Prohibition of Chemical Weapons that it had destroyed its chemical weapons in 2008.

And then there are North Korea's own nuclear weapons — the real wild card in the deck.

U.S. officials and other researchers say, North Korea may already have a few dozen warheads that could be fitted atop its vast fleet of ballistic missiles. They're fully capable of hitting targets in Japan, South Korea or elsewhere in the northern Pacific, the officials said.

Kim may be bluffing, as his father and grandfather did before him. But those weapons mean he must always be taken seriously.

Mission No. 1, Crowley said, is "figure out a way to denuclearize North Korea."