It's not so simple, as you think.
North Korea is brutal dictatorship since 1945 when Kim's grandfather become first president.
In the past they already invited South Korea, but America saved South at that time, by sending military troops.
Only reason why North Korea never invited South again is because of American military support last 60-70 years.
You can't blame the North Koreans for everything. I have noticed that in most of the cases, they are reacting to the provocations created by the Americans and the North Koreans. Perhaps the situation will improve, if the South is allowed to directly deal with the North.
I just shared simple facts.
North Korea invited South back in 1950.
America and UN saved South at that time, with military intervention of 16 countries under UN mandate.
The only reason why South Korea remained free land was due to US military protection.
So, we can't really say that North Korea is peaceful country.
There are numerous UN resolutions calling for the North Korea to stop a nuclear program that seriously endangers all neighbors, South Korea, Japan ... but without success.
So it can not be said that the international community didn't try to solve this problem, but North Korea refuses any cooperation with the international community (UN) and continually provokes and develops its nuclear program.
They do not want to talk directly to South Korea because they do not consider them as real country but American satellite.
In North Korea, one person decides about everything, including nuclear attack.
So, it's fact that North Korea is problem here, not vice versa.