Russia always wanted to sell its oil and gas to South Korea, with the best way to do that being pipelines across North Korea. Russia is trying to convince both Koreas to allow Russia to build the pipeline. Russia would also like to extend its railway to Seoul and eventually Busan on the southern edge of the Korean peninsula.
But then North Korea would be able to shut-off the oil whenever Kim Jong-un needed more lobster and fine French wine, similar to how Russia turned off the oil to Europe to spite Ukraine. Passengers and freight on the railway would be held hostage to Kim's whims.
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The DPRK declared: "Announcing the formal end to the Korean War was agreed at the North-South and the North-U.S. summits and is the first step towards reducing tension in the Korean peninsula and establishing a peace regime, It's required for building trust between the North and the U.S. Especially, the U.S. holds a responsibility and duty in declaring the end of the war."
However, the US did not actually agree in writing to sign a permanent peace treaty in the official statement from the June 12 summit, though US President Donald Trump might well have promised it verbally and South Korean President Moon Jae-in certainly promised it in his push for Sunshine Policy 2.0.
The June 12 official statement did note that "the DPRK commits to work toward complete denuclearization of the Korean Peninsula," but that's the usual ambiguous nonsense without any deadlines.
The DPRK is trying to force the US military off the Korean peninsula, the goal first established by Kim Jong-un's grandfather and founder of the DPRK, Kim Il-sung, so the DPRK can reunify the peninsula under brutal North Korean policies.
The US should counter with a specific timeline and definable goals, including unfettered, unannounced inspections of any facility within North Korea. Otherwise there's no point in considering a peace treaty.