You pretty much hit it on the head. It took the Germans 20 years and untold marks and Euros to get the East to where it is today, and it still is behind the West. Something like 10% of the population of the former DDR has moved west. The East is still somewhat disaffected. And as Squig points out, the differences between East and West were nothing compared to North and South Korea. I think the real answer for Korea is to find a nice pliant general who will knock off the Kims and in return for US troops leaving the South, the Chinese agree to the North becoming a protectorate of the South. Maybe after 50 years or so the country could then reunify, but frankly most of the generations that grew up under the Kims need to die off first.