SK vs NK

In Korean society (and Chinese) if you have a foreigner working for you or a guest of you, then their safety is your responsibility at the cost of your honor.  The principle wouldn't be able to live with himself if anything ever happened to one of us foreigner teachers.  Which is why he didn't like Michael riding a motorcycle.

The Chinese don't want the North Koreans starting a war.  So it won't be them who do.  That doesn't stop them from trying to provoke South Korea or America.  If North Korea can get someone else to start a war, then they will try.  But because of the Chinese, they themselves won't.  Especially right now with their important holiday and parade coming up.

Also, the North Koreans would have to be very careful is a war did start.  They couldn't harm a single Chinese person or China would be super angry.  That is why bombing Seoul wouldn't actually happen.  There are Chinese there.  No point in angering your only ally.  If there was a war, it would be only a ground war on their part.

The Chinese depend heavily on South Korean economy.  Since this is the 13 wealthiest nation in the world, we provide a huge benefit to the Chinese.  They would be pissed if that economic strength was threatened.  The greatest threat the North Koreans face at the moment is collapse.  They had two legs to stand on.  The first was giving the people food and aid that had been sponsored by the Soviet Union.  The second was protection from scary America.  The first leg is gone since the Soviet Union fell and that aid stopped coming in.  The only thing the North Korean government has left to offer is protection from America.  That won't be enough though if America stays backed off.  

North Korea is no longer a Communist country.  It is a black market country.  The government can try to appear to be strong.  However they are rapidly weakening and the South Koreans are watching to see how North Korea will collapse on itself.  They prefer if the civil war stays in North Korea or if they end up joining South Korea.  A united Korea is what both sides want, just not in the same way.

One goal the South Koreans desperately want is a united Korea.  One advantage to this is then they would finally be able to have a railway system run from South Korea all the way to Europe.  This is something that has been planned and worked on for years.  They even have the station set up and ready.