The expectation was that dividing Germany or Korea would be a temporary measure until a democratic government was formed. It was never intended to last even one decade. In Germany, three out of four occupied zones signed up for the democratic government which was formed in 1949, only 4 years after the end of the war. The agreed-upon plan was for Germany and Korea to form single, democratic governments, rendering the occupation zones a temporary measure. The fact on the ground was that the Soviets had millions of troops on the ground and surrendering all of Korea, or all of Germany to Stalin would have had grave consequences. No one likes being a divided country, but presumably the South Koreans prefer not being part of North Korea and the West Germans preferred not being part of the DDR.
In Germany's particular case, many of the allies were comfortable with the notion of dividing Germany anyway, since at least that way the Germans wouldn't start trying to conquer the rest of Europe again. But it wasn't the agreed plan, nor was it feasible to salvage the whole country as a democracy, either, nor did it seem wise to let Stalin have the whole country.
In Germany's particular case, many of the allies were comfortable with the notion of dividing Germany anyway, since at least that way the Germans wouldn't start trying to conquer the rest of Europe again. But it wasn't the agreed plan, nor was it feasible to salvage the whole country as a democracy, either, nor did it seem wise to let Stalin have the whole country.