Korea has been divided for nearly 20 years longer than Germany was, and the division was the result of the trusteeship of Korea (supposedly intended to last until an independent Korean government could be formed) becoming a tug of war between the U.S. and CCCP/PRC (resulting in the formation of competing and ideologically opposed governments)
Part of it is the fault of the South Koreans. Someone assassinated the only person with enough political power to assert that North and South needed to have a unified presidential election, and the other person pushed a South-only election, causing the Republic of Korea to get its first president (who also happened to be a dictator).
Might I remind you what happened when North and South Vietnam tried that strategy? Oh, right, massive war followed by communist victory. The latter obviously could not occur here, but it is just a bad strategy.
Kind of a moot point nowadays, though. The North Koreans are way, way,
way too afraid, brainwashed, and doublethought to participate in a free election even if it could be arranged.
If there is ever a Korean reunification, it won't happen for a long time. North and South Korea are, for the foreseeable future, better off as separate entities. If war happens the DMZ needs to stay up for at least a few years to get NK up to speed and keep China pacified.
I continue to hold the belief that all our problems would be solved by North Korea sinking into the ocean.