Reunification efforts in the late 1990s and early 2000s were complicated by the shift in US Policy from the Clinton to Bush Admin. Clinton's admin wanted to support the so called Sunshine Policy, which favored moving towards reunification.

For the US's part, they agreed to not re apply new sanctions on the North as long as the North continued to operate within the parameters of their Sunshine Policy negotiated with the South. That was what was happening, but then Bush came into office and this policy changed. New sanctions were put upon DPRK and they would eventually be included in the Bush Admin's "Axis of Evil" (Iran, Iraq, and North Korea).

This caused the North to go back on its agreements and the Sunshine Policy as a whole, and did also align with more conservative governments in South Korea.

All that said, I was smiling so big last night seeing the two leaders shaking hands, smiling themselves. A reunification of the 2 Koreas would be an absolute blessing upon the world. Many people in the North and South long to be reunited. Not to mention the ease of so many tensions in SE Asia that would come from 1 Korea.