But that's only because the conservative government that took power in South Korea took a hardline anti-unification stance and instead decided to strengthen relations with the US.

The US has a rich history of undermining unification processes. Like in 2005 when Bush Jr broke promises related to light-water reactors and the 2005 agreement (where North Korea would stop nuclear development in exchange for a non-aggression pact and relief from sanctions).

Or in March 2017 when the U.S. has dismissed a joint China-North Korea proposal where North Korea would end its nuclear weapons development in exchange for the U.S. stopping its military maneuvers with South Korea